Synthesis of biodiesel by using plasma electrolysis is very promising. This study aims to obtain high efficiency in the synthesis of biodiesel from palm oil by using cathodic plasma electrolysis method. The raw materials are palm oil, methanol, and KOH catalyst. Variations consist of cathode depth and oil-methanol molar ratio. The highest yield of 98.76% is obtained on the condition of cathode depth of 3.5 cm and oil:methanol molar ratio of 1:24. The lowest specific energy consumption of 605 J/ml is obtained on the condition of cathode depth of 3.5 cm and oil-methanol molar ratio of 1:12. High process efficiency is proved to be obtained by the use of cathodic plasma. These results indicate that cathodic plasma electrolysis method is effective to be used in the synthesis of biodiesel.