Through novel metallation reactions of active hydrogen compounds by lithium diisopropylamide, followed by coupling reactions between the carbanion and organosilyl chloride, new organosilicon-containing oligomers with reactive double bonds were synthesized. The silicon-containing oligomers obtained have ultra-violet (u.v.) crosslinking ability and can be expected as ultrathin films for gas separation membranes. Using 4-methylstyrene (MST) and/or allyltrimethylsilane (AS) as active hydrogen compounds, organosilicon-containing oligomers with reactive double bonds in the main chain and/or in the side chains were synthesized. By changing the molar ratio of MST/AS, it was found that the stiffness of the oligomers can be controlled. U.v. irradiation induced the crosslinking reactions of the organosilicon-containing oligomers with pendent vinyl groups.