p-(1H,1H,2H,2H-perfluorodecyloxydimethylsilyl)phenylacetylene(ACf8) and p-(1H,1H,2H,2H-Perfluorohexyloxydimethylsilyl)phenylacetylene(ACf4) were synthesized and copolymerized with p-trimethylsilylphenylacetylene(ASi). The resulting copolymers, copoly(ACf8/ASi) and copoly(ACf4/ASi), were fabricated to tough membranes showing high oxygen permeabilities(Po2) of 10(-8) cc(STP).cm/cm2.s.cmHg and high oxygen permselectivities(alpha=Po2PN2) of more than 2.7. In particular, a copoly(ACf4/ASi) containing 15.1 mol% of ACf4 unit showed the best result : Po2 = 3.51x10(-8) cc(STP).cm/cm2.s.cmHg and alpha = 3.04. The values were in a top level and very close to those of ’upper bound’ line in an alpha-Po2 plot of data in the literature. In addition, copoly(ACfn/ASi) membranes were ethanol permselective owing to water repellency of the perfluoroalkyl groups. Copoly(ACf4/ASi) membranes showed better oxygen and ethanol permselectivity than copoly(ACf8/ASi) membranes.