The Cenozoic basalts exposed in Bo Phloi Gem Field,Kanchanaburi Province,western Thailand are a host to different gem materials(e.g.,sapphire,black spinel,black pyroxene and zircon)as well as other xenocrysts and xenoliths from the deep-seated formations onto the earth surface.However,only felsic xenoliths have never been investigated and reported in detail though they are in fact significant evidence of ancient tectonic processes of this area.In this study,the felsic xenoliths were sampled and classified,on the basis of petrochemistry,into granite,syenogranite,and syenite.However,they contain similar mineral assemblages including essentials of quartz,K-feldspar,and plagioclase with different proportions and accessories of biotite,zircon,and opaque minerals.More-over,large phenocrysts of K-feldspar and plagioclase commonly present as a primary texture which are frequently corroded and replaced by\'sieved texture\'with secondary cumulative fringe of tiny feldspar and quartz.These secondary textures clearly indicate quenching after re-heating during transportation by basaltic magma.Geochemical analyses indicate that the alkaline and peraluminous magma show enrichment of Rb and depletion of Ba,Nb,Ta,Ti with steep slope of LREE/HREE en-richment patterns.These evidences suggest low-degree partial melting of crustal materials related to the collisional S-type granite magmatism.In addition,U-Pb dating of zircon from a felsic xenolith yields 211.6±1.3 Ma comparable to the Late Triassic magmatism of the central belt granite in this region which is resulted from the collision between Sibumasu and Indochina terranes.