This paper represents the first report on the peridotitic mantle xenoliths including spinel harzburgites and spinel lherzolites found in the Late Miocene-Pliocene basaltic rocks (Thracean alkaline basalts — TAB) of the Thrace region, northwestern Turkey. The lavas formed and extruded during the north-south extension of western Anatolia, are olivine basalts and basanites displaying within-plate affinity. The estimated modal mineralogy of the peridotite xenoliths is olivine (58–84 %) + orthopyroxene (12–35 %) + clinopyroxene (0–12 %) + spinel (1–5 %). They are characterized mainly by protogranular and also transitional protogranular to porphyroclastic and fine-grained equigranular textures. Melt pockets are recognized in only one sample. Deformation features in olivine and pyroxenes are zoning, twinning, including inclusions, kink banding, triple junction and undulatory extinction. Bulk-rock analyses indicate that the xenoliths are depleted in basaltic components (e.g. CaO — 0.39–1.50 wt. %, Al₂O₃ — 0.80–1.78 wt. %). Light rare-earth element (LREE) enrichment is significant (e.g. La_n 2–6), which suggests a cryptic metasomatic history.