A poly(o-trimethylsilylphenylacetylene) [poly(o-TMSPA)] initiated by a tungsten carbene complex was investigated under various conditions. The molar mass of poly(o-TMSPA) increases with increasing the polymerization temperature and decreasing the initiator concentration. The X-ray diffraction measurements show that poly(o-TMSPA) has an amorphous structure. The water molecules preferentially permeate through the poly(o-TMSPA) membranes. The effects of feed compositions, degree of swelling, and the molecular size of alcohols on the pervaporation performances were investigated. The separation factor and the permeation rate increase with increasing ethanol concentration in the feed. The diffusivity contributes to a major part to selective transport.