Animal fats are by-products from slaughterhouses that may be utilized as renewable energy source. This study was about biodiesel production from high free fatty acid beef tallow waste using two-step process with microwave heating. Sulfuric acid and NaOH were used as catalysts with methanol for the first esterification and second transesterification step, respectively. Catalyst loadings were between 0.25% and 2.5%, with applied microwave power of 340 W, operation time of 10-50 min, and oil-to-methanol molar ratio between 1:3 and 1:15. These process parameters were optimized using the design of experiments. The yields and properties of the biodiesel were assessed. The results indicated that the two-step process were successful in converting the beef tallow to biodiesel. Statistical analysis of the results showed that significant contributions were from the linear and quadratic terms of these three variables. The optimum conditions for esterification and transesterification were reported. Validity of the predicted models was confirmed by the experimental verification.