In order to prepare a genuine biodiesel, it is essential to use methanol prepared from biomass but not natural gas for biodiesel production. Thus, we have proposed to use crude bio-methanol produced by wood gasification for biodiesel production. Since such a bio-methanol contains some impurities, an effect of its impurities was studied on the biodiesel production by supercritical method. In general, impurities in crude bio-methanol are reported to include methyl formate, ethanol, I-butanol, diisopropyl ether, water, etc. Triglycerides and oleic acids were, thus, treated with these impurities under supercritical conditions. As a result, it was found that methyl formate, ethanol and 1-butanol could convert them to fatty acid alkyl esters (BDF), whereas no conversion was achieved with diisopropyl ether. Thus, crude bio-methanol can be used for BDF production as a substitute for methanol from fossil resources. However, due to more efficient reaction, crude bio-methanol can be more applicable to the two-step supercritical methanol process, consisting of hydrolysis of triglycerides and subsequent esterification of fatty acids, compared with the one-step supercritical methanol process, where transesterification of triglycerides is a major reaction. (c) 2007 Published by Elsevier Ltd.