Silicon-directed stereoselectivesyn addition of hydroxy group to olefinic double bond occurs intramolecularly in an acid-catalyzed cyclization of vinylsilanes bearing hydroxy group. Thus 5-dimethylphenylsilyl-4-penten-1-ol is smoothly cyclized to 2-(dimethylphenylsilyl)methyltetrahydrofuran upon the treatment of a catalytic amount ofp-toluenesulfonic acid (TsOH) or TiCl4.