diff --git a/beacon-chain/sync/validate_beacon_attestation.go b/beacon-chain/sync/validate_beacon_attestation.go
index 67953b9677..90d33ce2f0 100644
--- a/beacon-chain/sync/validate_beacon_attestation.go
+++ b/beacon-chain/sync/validate_beacon_attestation.go
@@ -268,10 +268,23 @@ func (s *Service) validateCommitteeIndexAndCount(
 	a eth.Att,
 	bs state.ReadOnlyBeaconState,
 ) (primitives.CommitteeIndex, uint64, pubsub.ValidationResult, error) {
-	// - [REJECT] attestation.data.index == 0
-	if a.Version() >= version.Electra && a.GetData().CommitteeIndex != 0 {
-		return 0, 0, pubsub.ValidationReject, errors.New("attestation data's committee index must be 0")
+	// Validate committee index based on fork.
+	if a.Version() >= version.Electra {
+		data := a.GetData()
+		attEpoch := slots.ToEpoch(data.Slot)
+		isGloas := attEpoch >= params.BeaconConfig().GloasForkEpoch
+		if isGloas {
+			if result, err := s.validateGloasCommitteeIndex(data); result != pubsub.ValidationAccept {
+				return 0, 0, result, err
+			}
+		} else {
+			// [REJECT] attestation.data.index == 0 (New in Electra, removed in Gloas)
+			if data.CommitteeIndex != 0 {
+				return 0, 0, pubsub.ValidationReject, errors.New("attestation data's committee index must be 0")
+			}
+		}
 	}
+
 	valCount, err := helpers.ActiveValidatorCount(ctx, bs, slots.ToEpoch(a.GetData().Slot))
 	if err != nil {
 		return 0, 0, pubsub.ValidationIgnore, err
@@ -356,6 +369,29 @@ func validateAttestingIndex(
 	return pubsub.ValidationAccept, nil
 }
 
+// validateGloasCommitteeIndex validates committee index rules for Gloas fork.
+// [REJECT] attestation.data.index < 2. (New in Gloas)
+// [REJECT] attestation.data.index == 0 if block.slot == attestation.data.slot. (New in Gloas)
+func (s *Service) validateGloasCommitteeIndex(data *eth.AttestationData) (pubsub.ValidationResult, error) {
+	if data.CommitteeIndex >= 2 {
+		return pubsub.ValidationReject, errors.New("attestation data's committee index must be < 2")
+	}
+
+	// Same-slot attestations must use committee index 0
+	if data.CommitteeIndex != 0 {
+		blockRoot := bytesutil.ToBytes32(data.BeaconBlockRoot)
+		slot, err := s.cfg.chain.RecentBlockSlot(blockRoot)
+		if err != nil {
+			return pubsub.ValidationIgnore, err
+		}
+		if slot == data.Slot {
+			return pubsub.ValidationReject, errors.New("same slot attestations must use committee index 0")
+		}
+	}
+
+	return pubsub.ValidationAccept, nil
+}
+
 // generateUnaggregatedAttCacheKey generates the cache key for unaggregated attestation tracking.
 func generateUnaggregatedAttCacheKey(att eth.Att) (string, error) {
 	var attester uint64
diff --git a/beacon-chain/sync/validate_beacon_attestation_test.go b/beacon-chain/sync/validate_beacon_attestation_test.go
index 45b066bea8..7067354a14 100644
--- a/beacon-chain/sync/validate_beacon_attestation_test.go
+++ b/beacon-chain/sync/validate_beacon_attestation_test.go
@@ -684,3 +684,75 @@ func Test_validateCommitteeIndexAndCount_Boundary(t *testing.T) {
 	require.ErrorContains(t, "committee index", err)
 	require.Equal(t, pubsub.ValidationReject, res)
 }
+
+func Test_validateGloasCommitteeIndex(t *testing.T) {
+	tests := []struct {
+		name           string
+		committeeIndex primitives.CommitteeIndex
+		attestationSlot primitives.Slot
+		blockSlot      primitives.Slot
+		wantResult     pubsub.ValidationResult
+		wantErr        string
+	}{
+		{
+			name:           "committee index >= 2 should reject",
+			committeeIndex: 2,
+			attestationSlot: 10,
+			blockSlot:      10,
+			wantResult:     pubsub.ValidationReject,
+			wantErr:        "committee index must be < 2",
+		},
+		{
+			name:           "committee index 0 should accept",
+			committeeIndex: 0,
+			attestationSlot: 10,
+			blockSlot:      10,
+			wantResult:     pubsub.ValidationAccept,
+			wantErr:        "",
+		},
+		{
+			name:           "committee index 1 different-slot should accept",
+			committeeIndex: 1,
+			attestationSlot: 10,
+			blockSlot:      9,
+			wantResult:     pubsub.ValidationAccept,
+			wantErr:        "",
+		},
+		{
+			name:           "committee index 1 same-slot should reject",
+			committeeIndex: 1,
+			attestationSlot: 10,
+			blockSlot:      10,
+			wantResult:     pubsub.ValidationReject,
+			wantErr:        "same slot attestations must use committee index 0",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockChain := &mockChain.ChainService{
+				BlockSlot: tt.blockSlot,
+			}
+			s := &Service{
+				cfg: &config{
+					chain: mockChain,
+				},
+			}
+
+			data := &ethpb.AttestationData{
+				Slot:            tt.attestationSlot,
+				CommitteeIndex:  tt.committeeIndex,
+				BeaconBlockRoot: bytesutil.PadTo([]byte("blockroot"), 32),
+			}
+
+			result, err := s.validateGloasCommitteeIndex(data)
+
+			require.Equal(t, tt.wantResult, result)
+			if tt.wantErr != "" {
+				require.ErrorContains(t, tt.wantErr, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
diff --git a/changelog/terence_gloas-attestation-validation.md b/changelog/terence_gloas-attestation-validation.md
new file mode 100644
index 0000000000..94749d9328
--- /dev/null
+++ b/changelog/terence_gloas-attestation-validation.md
@@ -0,0 +1,3 @@
+### Added
+
+- Add gossip beacon attestation validation conditions for Gloas fork