Conversion of waste edible oil to the fatty acid methyl esters was optimized using sulfuric acid as a catalyst for transesterification and esterification simultaneously, and adding tetrahydrofuran as a cosolvent for producing a homogeneous media. The optimized model was established by the response surface methodology. The optimum conditions were methanol/oil molar ratio of 21:1, 3.95% of sulphuric acid based on the oil mass, and reaction period of 3.3 h at 64 C in the presence of tetrahydrofuran, obtaining a fatty acid methyl esters yield of 98.2%. Further verification experiments confirmed the validity of the predicted model. The result suggested that the present work had a significantly lower reaction temperature and methanol/oil molar ratio by the addition of tetrahydrofuran to the reaction system.