Abstract: Mercapto polysilsesquioxane and mercapto-phenyl polysilsesquioxane were synthesized with mercapto propyl trimethoxysilane and phenyl trimethoxy silane as raw materials,methanol as solvent and concentrated HCl as catalyst. The products were characterized by FTIR and GPC. The results showed that when the phenyl monomer addition amount was 20%,the products contained a certain amount of mercapto and phenyl,improved the refractive index while retained the active sulfydryl. The relative molecular mass was large and the distribution narrow.