A novel organic silicon compound having at least one .tbd.SiH group in a molecule and a fluorinated organic group at either end is a useful crosslinking agent for various resins, especially fluorinated resins. An organopolysiloxane composition comprising (A) an organopolysiloxane having in a molecule at least two alkenyl groups and at least one fluorinated substituent, (B) an organohydrogenpolysiloxane having at least two .tbd.SiH groups in a molecule and a fluorinated organic group at either end, and (C) a platinum catalyst is readily curable to products having solvent and moisture resistance.