A novel process has been discovered for the production of glyoxylic acid. When the ozonolysis of maleic acid was conducted in solvents that contained methanol, acetic acid, or formic acid at approximately -5 degrees C, hydroperoxide compounds and glyoxylic acid hemiacetal were formed in high yield (> 95%). The prepared mixture then was dropped into a glyoxal solution (the molar ratio of maleic acid and glyoxal was slightly greater than 1: 1) that had been warmed to similar to 38 degrees C. Glyoxal was oxidized by the hydroperoxides in the mixture via a Baeyer-Villiger rearrangement. When the reaction ended, some water was added to the solution and organic solvents were distilled off at reduced pressure at 50 degrees C. An aqueous solution of glyoxylic acid was obtained. Through this procedure, both maleic acid and glyoxal were converted to glyoxylic acid.