It was found that oxalic acid is one of the main products in the Briggs-Rauscher oscillating reaction. In nonoscillating solutions, oxidation of iodomalonic acid and/or diiodomalonic acid by Fenton-type reactions also produced oxalic acid as well as I-2. Mesoxalic acid yielded oxalic acid under similar conditions. Tartronic acid was nearly inert to Fenton-type reactions; however, tartronic acid was oxidized by iodate and iodine to mesoxalic acid, which in turn could form oxalic acid in the presence of H2O2 plus catalyst. Iodotartronic acid appeared to be a short-lived but significant intermediate, thus both tartronic acid and mesoxalic acid are possible intermediates. Glycolic acid and glyoxylic acid are not intermediates in the oxidation of iodomalonic acid, since they in turn produce formic acid under similar nonoscillating conditions.