Transesterification of beef tallow and methanol is affected by many factors. Catalyst, free fatty acids, and water in beef tallow, and reaction time were investigated. Sodium hydroxide (NUOH) was a more effective catalyst than sodium methoxide (NaMeOj. NaOH and NaMeO reached their maximum activities at 0.3% and 0.5%, w/w of beef tallow, respectively. The presence of water had more negative effect on transesterification than did the presence of free fatty acids (FFA). For best results, the water content of beef tallow should be kept not beyond 0.0696, w/w. FFA content of beef tallow should be kept below 0.596, w/w. The transesterification of beef tallow was very slow in the first minute. The production of beef tallow methyl esters (BTME) was complete after about 15 min. There were still some mono- and diglycerides in the BTME phase after the reaction was finished