Poly(phenylsilsesquioxane) (PSQ) having tributylstannyl groups (TBPSQ) was prepared from phenyltrimethoxysilane and bis(tributyltin) oxide [(Bu3Sn)(2)O] under basic conditions. The procedure, using a catalytic amount of basic reagent such as triethylamine, sodium hydroxide, or aqueous ammonia., afforded yields of TBPSQ based on Si in the range of 12-45% at a number-average molecular weight precipitated from ethanol of about 3500. In the other procedure, starting from PSQ with (Bu3Sn)(2)O, the incorporation of tributylstannyl groups into PSQ proceeded effectively in the presence of an acid catalyst such as methanesulfonic acid or sulfuric acid, giving TBPSQ in moderate yields of greater than 52%. Dibutyltin oxide, a bifunctional organotin compound, was also used, affording dibutylstannylated poly(phenylsilsesquioxane) (DBPSQ) without crosslinking. The highest ratio of Si and Sn contained in TBPSQ or DBPSQ, prepared under acidic conditions, was Si/Sn = 7/1.