In this study, the transesterification of cottonseed oil with methanol was carried out using NaOH. The parameters, such as molar methanol: oil ratio, NaOH%, and temperature effecting the yield and biodiesel quality, were investigated to optimize biodiesel production from cottonseed oil. Below 50 degrees C, transesterification of cottonseed oil was not completed at any molar methanol: oil ratios and catalyst percentages in 1 h. In 3:1 methanol:oil ratio, full conversion was not observed. Optimum conversion was obtained at 6:1 methanol:oil ratio and at temperatures between 50 and 60 degrees C. Above 60 degrees C, some difficulties were encountered in the washing step. Biodiesels that were produced at different molar methanol:oil ratios, NaOH concentrations, and temperatures were tested according to accepted standard methods and the results were compared with standard values.