In the ethanol/water pervaporation using membranes of Si-containing polymers, poly[1-phenyl-2-(p-trimethylsilyl)phenylacetylene] and poly[1-beta-naphthyl-2-(p-trimethylsilyl)phenylacetylene], these polymer membranes permeated ethanol preferentially; alpha(EtOH/H2O) 6.86 and 5.30, respectively, at 10 wt% EtOH content in the feed. Membranes of hydrocarbon-based polymers, poly diphenylacetylene) and poly(1-beta-naphthyl-2-phenylacetylene), which were prepared by desilylation of the two Si-containing polymer membranes, also exhibited ethanol permselectivity in ethanol/water pervaporation; (alpha(EtOH/H2O) 5.95 and 3.79, respectively. Further, in benzene/cyclohexane pervaporation, these desilylated membranes, which were insoluble in any organic solvent, showed rather low benzene permselectivity but very large fluxes. The results of the present study are attributed to the presence of many microvoids and, in turn, sparse structures.