The solubility and extractability of alcohol to triglyceride is an important factor in biodiesel production to enhance the reaction rate and to obtain a better purification. Methanol and isopropanol have an opposite properties of solubility and extractability to Jatropha curcas oil. Therefore, the mixture of methanol and isopropanol was used for conducting in situ transesterification of Jatropha curcas seeds with sodium methoxide as alkaline catalyst. The reaction was carried out by varying the ratio of solvent volume to seed weight from 6.25 to 8.75 (ml/g), various volume ratio of methanol to mixture from 0.33 to 0.66 (ml MeOH/ml mixture), and various catalyst concentration from 1.0 to 2.0 wt at 60°C and reaction time 120 minutes. The highest conversion to biodiesel 74.28 was achieved with ratio of methanol and isopropanol volume to seed weight of 7.39, volume ratio of methanol to mixture of 0.655 and NaOMe concentration 1.58 wt at 60°C and reaction time 120 minutes. © 2011 IEEE.