This study compared formation and degradation behaviors of organic acids in landfill leachate under microwave oxidation process (MOP) and under conventional heating oxidation (CHO) and explored derivative mechanisms of organic acids in MOP. The results showed that formation and degradation behaviors of oxalic acid were very similar under CHO and MOP, in which its concentrations decreased in the temperature-raising period, then increased due to decomposition of TOC from 10 to 70 min, decreased due to persulfate oxidation from 70 to 130 min, and stayed the same afterwards. The pH values of the leachate solution dropped 0.51 and 0.65 pH units after MOP and CHO treatment, respectively. Oxalic acid was the dominant organic acid formed in MOP. The derivative mechanisms of organic acids were developed using the experimental results. Lactic acid was generated from decomposition of malic acid, and oxalic acid was formed from oxidation of its precursors. Acetic acid was formed and soon decomposed. Lactic acid had its maximum concentration with a persulfate dose of 0.5 M, while lower or higher persulfate doses yielded few or no lactic acid in MOP. (c) 2013 Elsevier B.V. All rights reserved.