Three types of homopolymerizations of p-(dimethylsilyl)-phenylacetylene (HSPA) having a terminal triple bond and a Si-H group were selectively carried out by using three kinds of polymerization catalysts. Among them poly(HSPA) synthesized by addition polymerization of its triple bond using [Rh(nbd)Cl](2) (nbd: norbornadiene)/phenylethylamine (PEA) showed a good membrane forming ability. The copolymerizations of HSPA with p-(trimethylsilyl)phenylacetylene (SPA) were carried out using [Rh(nbd)Cl](2)/PEA and the resulting copolymers were fabricated to self-supporting membranes. These membranes, including the homopolymer of HSPA, showed higher permselectivities for oxygen and carbon dioxide over nitrogen than those of poly(SPA). Incorporation of HSPA unit to poly(SPA) effectively enhanced its permselectivities with only small decrease in its permeability.