Rapeseed is one of the important vegetable oil sources for biodiesel production due to its high oil content (around 40%). In this study rapeseed oil was converted to biodiesel by transesterification using microwave heating. Experiments were carried out in the presence of two different alkali catalysts which are sodium hydroxide and potassium hydroxide. Effects of various reaction parameters such as catalyst ratio, reaction temperature and time were investigated. Mono-, di- and triglyceride content of biodiesel were determined by gas chromatography analysis. Yield and purity (ester content) percentages of biodiesel were specified in weight, which are 88.3-93.7% and 87.1-99.4%, respectively. The results indicated that microwave heating has effectively increased the biodiesel yield and decreased the reaction time. (c) 2007 Elsevier Ltd. All rights reserved.