Catalyzed by Lewis acid, 1,2-diphenyldiselane or 1,2-di-p-tolyldisulfane could add to methylenecyclopropanes smoothly. Compared with the reported free radical additions, the results were quite different. A four-membered carbon ring was constructed to give cyclobutane-1,1-diylbis(phenylselane) derivatives or cyclobutane-1,1-diylbis(p-tolylsulfane) derivatives as products, which are useful intermediates in organic synthesis.