The photochemicalringexpansion of dispirosubstitutedcyclobutane-1,3-diones in methanol has been investigated. The formation of ringexpansion product was strongly dependent on the spiro ring size of dispiro substituent. The ring expanded acetal was obtained in a low yield when the spiro ring of dispirosubstitutedcyclobutane-1,3-diones was a five- or seven-membered ring. This is the first example