Enhanced oxalic acid production was investigated in semi-solid state fermentation of methanol-resistant Aspergillus niger using corncob. Methanol-resistant A.niger was selected from the sector of colony showing phenotypically intact growth despite 5% methanol in solid medium (PDA) and finally obtained through the adaptation process for 22 weeks. Oxalic acid production of methanol-resistant A. niger was dramatically enlarged in liquid culture (CZB) by 9.14 folds compared with that of parent cells. Semi-solid state fermentation of corncob has been developed for the application of low-cost and environment friendly biomass waste to organic acid production. Oxalic acid production was dependent of inoculum size and initial substrate concentration, which was optimized at 10(6) spores/g dry weight and 5% (w/v) corncob in 0.1 N NaOH solution, respectively, which led to the maximum productivity (123.0 g/kg dry weight of corncob). Results demonstrate that methanol-resistant A. niger has great potentials for oxalic acid production from biomass. (C) 2015 Elsevier Ltd. All rights reserved.