The surface structure of fluorinated poly(imidesiloxane)s (FSIM) with different segment lengths and contents of siloxane was investigated by ATR-FTIR and X-ray photoelectron spectroscopy. Although fluorine and siloxane compounds have low surface energies, the surface composition of FSIM was strongly affected by their segment length. The longer segment length is, the higher surface segregation is. This indicates that the long segment has strong driving force to the surface.