L-Gulonolactone (I) was condensed with benzaldehyde to afford mono- and di-O-benzylidene-L-gulonolactone. Mono-O-benzylidene-L-gulonolactone (II) was not oxidized by periodic acid, while its amide was oxidized extremely slowly by periodic acid. II was reduced by sodium borohydride to yield 2, 4-O-benzylidene-D-sorbitol. Therefore, the structure of II was established as 3, 5-O-benzylidene-L-gulonolactone. Di-O-benzylidene-L-gulonolactone (III) was partially hydrolyzed by acid to II. III did not react with ammonia in methanol and was recovered from the reaction mixture. Based on the result of acid hydrolysis of III and from the conformational consideration, it was concluded that III is 2, 6 : 3, 5-di-O-benzylidene-L-gulonolactone.