Polymethylsilsesquioxane (PMS) and polyvinylsilsesquioxane (PVS) were prepared by acid-catalyzed controlled hydrolytic polycondensation of methyl- and vinyltrimethoxysilane (MTS and VTS), respectively. The spinnabilities and molecular weights of polysilsesquioxanes were easily controlled by the reaction conditions, such as the molar ratios of water, hydrochloric acid, and methanol to MTS or VTS; nitrogen flow rate; temperature; and stirring rate. PMS and PVS showed spinnability of more than 200 cm when their molecular weights were up to 42,000 (PMS) and 19,000 (PVS) M-w. Transparent, colorless, and flexible films of 0.02-0.10 mm thick were prepared by casting a 20 wt % acetone-methanol (V/V = 1) solution of PMS and PVS on a polymethylpentene shale, followed by heating at 80 degrees C for 3 weeks. The tensile strength of the films, approximately 26 (PMS) and 17 (PVS) MPa, was found to be correlated with the structure of the polysilsesquioxanes. The surface contact angle and electroconductivity of films were also measured.