diff --git a/zaban_backend/app/api/v1/voiceprint.py b/zaban_backend/app/api/v1/voiceprint.py
index 4c3b3ab..f7df806 100644
--- a/zaban_backend/app/api/v1/voiceprint.py
+++ b/zaban_backend/app/api/v1/voiceprint.py
@@ -34,6 +34,11 @@ def get_verifier(request: Request):
     return verifier
 
 
+def get_diarization_service(request: Request):
+    """Dependency to get the diarization service from app state."""
+    return getattr(request.app.state, "diarization_service", None)
+
+
 def _service_unavailable_response() -> JSONResponse:
     """Return a graceful response when voiceprint service is unavailable."""
     if not settings.VOICEPRINT_ENABLED:
@@ -121,7 +126,8 @@ async def verify_voiceprint(
     device_id: Optional[str] = Form(None),
     file: UploadFile = File(None),
     db: Session = Depends(get_db),
-    verifier=Depends(get_verifier)
+    verifier=Depends(get_verifier),
+    diarization_service=Depends(get_diarization_service)
 ):
     """Verify a user's voice against their enrolled voiceprint."""
     if verifier is None:
@@ -147,6 +153,23 @@ async def verify_voiceprint(
         async with await open_file(temp_path, "wb") as f:
             await f.write(audio_content)
 
+        # Diarization check (ensure single speaker)
+        if diarization_service:
+            # Run diarization in executor as it's CPU/GPU heavy
+            import asyncio
+            loop = asyncio.get_running_loop()
+            diarization_result = await loop.run_in_executor(
+                None, diarization_service.diarize, temp_path
+            )
+            
+            unique_speakers = len(set(segment["speaker"] for segment in diarization_result))
+            if unique_speakers > 1:
+                return VerificationResponse(
+                    verified=False,
+                    threshold=settings.VERIFICATION_THRESHOLD,
+                    error=f"Multiple speakers detected ({unique_speakers}). Please provide audio with only one speaker."
+                )
+
         # Verify
         result = await verifier.verify_speaker(temp_path, str(customer_id))
         
diff --git a/zaban_backend/app/main.py b/zaban_backend/app/main.py
index 32ea699..336a095 100644
--- a/zaban_backend/app/main.py
+++ b/zaban_backend/app/main.py
@@ -64,6 +64,17 @@ async def startup_event():
     else:
         print("ℹ️  Voiceprint service disabled (VOICEPRINT_ENABLED=false)")
 
+    # Initialize Diarization Service
+    try:
+        from .services.diarization.service import DiarizationService
+        app.state.diarization_service = DiarizationService()
+        print("✅ Diarization service initialized.")
+    except Exception as e:
+        import traceback
+        print(f"⚠️  Diarization service initialization failed: {e}")
+        traceback.print_exc()
+        app.state.diarization_service = None
+
 
 @app.get("/up")
 async def up():
diff --git a/zaban_backend/app/services/diarization/clustering.py b/zaban_backend/app/services/diarization/clustering.py
new file mode 100644
index 0000000..bead967
--- /dev/null
+++ b/zaban_backend/app/services/diarization/clustering.py
@@ -0,0 +1,69 @@
+# app/services/diarization/clustering.py
+
+from sklearn.cluster import AgglomerativeClustering
+import numpy as np
+from sklearn.metrics.pairwise import cosine_similarity
+
+def is_single_speaker(embeddings, threshold=0.75):
+    """
+    Check if all embeddings are similar → single speaker
+    """
+    if len(embeddings) < 2:
+        return True
+
+    sims = cosine_similarity(embeddings)
+
+    # ignore diagonal
+    avg_sim = (np.sum(sims) - len(sims)) / (len(sims)**2 - len(sims))
+
+    return avg_sim > threshold
+
+class SpeakerClustering:
+    def __init__(self, distance_threshold=0.6, single_speaker_threshold=0.7):
+        """
+        distance_threshold: For AgglomerativeClustering (1 - cosine_similarity)
+        single_speaker_threshold: Cosine similarity threshold for Pre-Diarization Decision Layer
+        """
+        self.distance_threshold = distance_threshold
+        self.single_speaker_threshold = single_speaker_threshold
+
+    def cluster(self, segments):
+        """
+        segments: [{start, end, embedding}]
+        """
+        if not segments:
+            return []
+
+        embeddings = np.array([s["embedding"] for s in segments])
+        
+        # Normalize embeddings for cosine distance
+        norms = np.linalg.norm(embeddings, axis=1, keepdims=True)
+        norms[norms == 0] = 1.0  # avoid division by zero
+        embeddings = embeddings / norms
+
+        # Pre-Diarization Decision Layer
+        if is_single_speaker(embeddings, threshold=self.single_speaker_threshold):
+            print(f"Single speaker detected (sim > {self.single_speaker_threshold}). Skipping clustering.")
+            for seg in segments:
+                seg["speaker"] = "speaker_0"
+            return segments
+
+        # Clustering for multiple speakers
+        try:
+            clustering = AgglomerativeClustering(
+                n_clusters=None,
+                distance_threshold=self.distance_threshold,
+                metric="cosine",
+                linkage="average"
+            )
+            labels = clustering.fit_predict(embeddings)
+        except Exception as e:
+            print(f"Clustering failed: {e}. Falling back to single speaker.")
+            for seg in segments:
+                seg["speaker"] = "speaker_0"
+            return segments
+
+        for seg, label in zip(segments, labels):
+            seg["speaker"] = f"speaker_{label}"
+
+        return segments
\ No newline at end of file
diff --git a/zaban_backend/app/services/diarization/config.py b/zaban_backend/app/services/diarization/config.py
new file mode 100644
index 0000000..e69de29
diff --git a/zaban_backend/app/services/diarization/pipeline.py b/zaban_backend/app/services/diarization/pipeline.py
new file mode 100644
index 0000000..3ff986d
--- /dev/null
+++ b/zaban_backend/app/services/diarization/pipeline.py
@@ -0,0 +1,91 @@
+# app/services/diarization/pipeline.py
+
+import torch
+import librosa
+from speechbrain.inference import EncoderClassifier
+from speechbrain.inference.VAD import VAD
+
+
+class DiarizationPipeline:
+    def __init__(self):
+        # Speaker embedding model (ECAPA)
+        self.embedding_model = EncoderClassifier.from_hparams(
+            source="speechbrain/spkrec-ecapa-voxceleb",
+            run_opts={"device": "cpu"}
+        )
+
+        # Voice Activity Detection
+        self.vad = VAD.from_hparams(
+            source="speechbrain/vad-crdnn-libriparty",
+            run_opts={"device": "cpu"}
+        )
+
+    def load_audio(self, path):
+        waveform, sr = librosa.load(path, sr=16000)
+        return torch.tensor(waveform).unsqueeze(0), sr
+
+    def get_speech_segments(self, audio_path):
+        """
+        Returns speech segments [(start, end)]
+        """
+        boundaries = self.vad.get_speech_segments(audio_path)
+        segments = []
+
+        for seg in boundaries:
+            start = float(seg[0])
+            end = float(seg[1])
+            segments.append((start, end))
+        print("VAD output:", boundaries)
+
+        return segments
+
+    def get_embedding(self, waveform):
+        """
+        Extract speaker embedding
+        """
+        with torch.no_grad():
+            emb = self.embedding_model.encode_batch(waveform)
+        return emb.squeeze().numpy()
+
+    def extract_embeddings(self, audio_path, segments):
+        waveform, sr = self.load_audio(audio_path)
+
+        embeddings = []
+
+        CHUNK_DURATION = 1.5  # seconds
+        STRIDE = 0.75         # overlap
+
+        chunk_size = int(CHUNK_DURATION * sr)
+        stride_size = int(STRIDE * sr)
+
+        for start, end in segments:
+            duration = end - start
+            start_sample = int(start * sr)
+            end_sample = int(end * sr)
+            segment_wave = waveform[:, start_sample:end_sample]
+
+            if segment_wave.shape[1] == 0:
+                continue
+
+            # If segment is shorter than chunk_size, take the whole segment
+            if duration < CHUNK_DURATION:
+                emb = self.get_embedding(segment_wave)
+                embeddings.append({
+                    "start": start,
+                    "end": end,
+                    "embedding": emb
+                })
+                continue
+
+            # For longer segments, use sliding window
+            for i in range(0, segment_wave.shape[1] - chunk_size + 1, stride_size):
+                chunk = segment_wave[:, i:i + chunk_size]
+                
+                emb = self.get_embedding(chunk)
+                embeddings.append({
+                    "start": start + (i / sr),
+                    "end": start + (min(i + chunk_size, segment_wave.shape[1]) / sr),
+                    "embedding": emb
+                })
+
+        return embeddings
\ No newline at end of file
diff --git a/zaban_backend/app/services/diarization/segmenter.py b/zaban_backend/app/services/diarization/segmenter.py
new file mode 100644
index 0000000..e0057b4
--- /dev/null
+++ b/zaban_backend/app/services/diarization/segmenter.py
@@ -0,0 +1,77 @@
+# app/services/diarization/segmenter.py
+
+class Segmenter:
+    @staticmethod
+    def resolve_overlaps(segments):
+        """
+        Convert overlapping segments into timeline using majority voting
+        """
+        timeline = []
+
+        for seg in segments:
+            timeline.append((seg["start"], "start", seg["speaker"]))
+            timeline.append((seg["end"], "end", seg["speaker"]))
+
+        timeline.sort()
+
+        active = []
+        result = []
+
+        last_time = None
+
+        for time, typ, speaker in timeline:
+            if last_time is not None and active:
+                # pick most frequent speaker
+                speaker_counts = {}
+                for s in active:
+                    speaker_counts[s] = speaker_counts.get(s, 0) + 1
+
+                dominant = max(speaker_counts, key=speaker_counts.get)
+
+                result.append({
+                    "start": last_time,
+                    "end": time,
+                    "speaker": dominant
+                })
+
+            if typ == "start":
+                active.append(speaker)
+            else:
+                if speaker in active:
+                    active.remove(speaker)
+
+            last_time = time
+
+        return result
+    
+    @staticmethod
+    def merge_segments(segments, gap_threshold=0.5):
+        if not segments:
+            return []
+
+        segments = sorted(segments, key=lambda x: x["start"])
+        merged = [segments[0]]
+
+        for current in segments[1:]:
+            last = merged[-1]
+
+            if (
+                current["speaker"] == last["speaker"]
+                and (current["start"] - last["end"]) <= gap_threshold
+            ):
+                last["end"] = current["end"]
+            else:
+                merged.append(current)
+
+        return merged
+
+    @staticmethod
+    def format_output(segments):
+        return [
+            {
+                "start": s["start"],
+                "end": s["end"],
+                "speaker": s["speaker"]
+            }
+            for s in segments
+        ]
\ No newline at end of file
diff --git a/zaban_backend/app/services/diarization/service.py b/zaban_backend/app/services/diarization/service.py
new file mode 100644
index 0000000..ba59c8e
--- /dev/null
+++ b/zaban_backend/app/services/diarization/service.py
@@ -0,0 +1,37 @@
+# app/services/diarization/service.py
+
+from .pipeline import DiarizationPipeline
+from .clustering import SpeakerClustering
+from .segmenter import Segmenter
+
+
+class DiarizationService:
+    def __init__(self, distance_threshold=0.6, single_speaker_threshold=0.7):
+        self.pipeline = DiarizationPipeline()
+        self.clustering = SpeakerClustering(
+            distance_threshold=distance_threshold,
+            single_speaker_threshold=single_speaker_threshold
+        )
+
+    def diarize(self, audio_path: str):
+        """
+        Full diarization pipeline
+        """
+
+        # Step 1: VAD → segments
+        segments = self.pipeline.get_speech_segments(audio_path)
+
+        # Step 2: embeddings
+        segments_with_embeddings = self.pipeline.extract_embeddings(
+            audio_path, segments
+        )
+
+        # Step 3: clustering → assign speakers
+        clustered = self.clustering.cluster(segments_with_embeddings)
+
+        # Step 4: merge segments
+        resolved = Segmenter.resolve_overlaps(clustered)
+        merged = Segmenter.merge_segments(resolved)
+
+        # Step 5: format output
+        return Segmenter.format_output(merged)
\ No newline at end of file
diff --git a/zaban_backend/app/services/diarization/utils/audio.py b/zaban_backend/app/services/diarization/utils/audio.py
new file mode 100644
index 0000000..e69de29
diff --git a/zaban_backend/app/services/diarization/utils/embeddings.py b/zaban_backend/app/services/diarization/utils/embeddings.py
new file mode 100644
index 0000000..e69de29