It was found that a lactone ring was esterified to a methyl ester group in the bufferized methanol containing triethylamine-acetic acid or sodium acetate without simultaneous cleavage of the acyl groups and the methyl ester groups and this methanolysis mainly proceeded without acyl migration. Using this method, 2, 4-O-benzylidene-5-O-acyl-D-glucaro-6, 3-lactone 1-methyl esters (II, III, IV and V) were esterified in excellent yields to dimethyl 2, 4-O-benzylidene-5-O-acyl-D-glucarates (VII, VIII, IX and X respectively), and from the latters, dimethyl 2, 4-O-benzylidene-3-O-acetyl-5-O-acyl-D-glucarates (XI, XII, XIII and XIV respectively) were synthesized by the usual acetylation. Moreover, 1, 2-O-isopropylidene-5-O-acetyl-D-glucofuranurono-6, 3-lactone (XIX) could be also esterified to methyl 1, 2-O-isopropylidene-5-O-acetyl-D-glucofuranuronate (XX) by the same method.