Abstract: Polystyrene,cross-linked with 5-7% of divinylbenzene,is combined with TiCl₄ in CS₂ to form a stable complex containing 4.5% of chlorine. The TiCl₄ complexed in the polymer is resistant to water and can store in air at least for one year. The Lewis acid complex catalyst can be used to catalyze the conversion of aromatic aldehydes,carboxylic acids,ketones and some alcohols into corresponding acetals,esters,ketals and ethers in hish yield. The complex is also effective for the Friedel-Crafts alkylation reaction. For these reactions the title catalyst can be used repeatedly 4-5 times.