The surface compositions of a series of block and graft copolymers of polystyrene-polydimethylsiloxane was investigated by attenuated total reflectance(ATR-FTIR)and X-ray photoelectron spectroscopy(XPS).It was shown that enrichment of PDMS soft segments occurred on the surface of the block copolymers as well as on that of graft copolymers．The degree of enrichment of PS-b-PDMS was larger than that of PS-g-PDMS

which was explained as a result of the easiness of movement of the PDMS segments of PS-b-PDMS．Meanwhile．the solvents of different solubility parameter and the contact medium of different polarity had different influence on the enrichment of PDMS on the surface．The surface energy measurement further confirmed that the diblock copolymers tended to have higher surface enrichment of the PDMS segments than that of the graft copolymers．