Esterification of free fatty acids (FFA) in waste cooking oil and transesterification with ethanol using concentrated H2SO4 and NaOH as homogeneous catalysts, respectively, were studied in order to find optimal conditions. Waste cooking oils collected from small and fast-food restaurants such as KFC, Lotteria having relatively high acid numbers, 25.2 mg KOH/g were converted into biodiesel by the two-stage method. The optimal condition for the first stage: mol ratio ethanol:FFA = 50:1, at 70°C, 5wt percent H2SO4 for reaction time of 120 minutes, the acid number has dropped to 1.8 mg KOH/g. The transesterification was taken place in two steps, each step followed by ethanol evaporation under vacuum pressure then glycerol extraction. The recuperated ethanol was reused for next batchs so that production cost could be reduced significantly. The optimum for transesteification was mole ratio ethanol:oil = 9: 1, at 70°C, 0.8 wt percent NaOH with reaction time of 60 minutes for each step. The final product contained 99.5 percent ethyl ester in accordant with EN 14214 standard.