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 pyroxeres 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.