Biodiesel, an alternative fuel similar to fossil-based diesel, has the advantages of carbon-neutral, high flash point and emit no carbon dioxide (CO2). HHO gas has been introduced to the automotive industry as a new energy source, a fuel supplement in an internal combustion engine (IC). This paper presents the performance and emissions of diesel engines powered by biodiesel with HHO gas as a fuel supplement. The biodiesel used is a mixture of biodiesel B20 and B30. The effect of adding HHO gas on biodiesel fuel is evaluated on engine performance and emissions before and after using HHO gas as a secondary fuel. The results show an increase in engine performance on the B20 is 14% and on the B30 is 14.63%. The observation on smoke produce of the tailpipe exhaust also drastically improved. Based on the results above, that the addition of HHO gas supplements to biodiesel fuel has a positive effect on improving engine performance and reducing emissions that are very significant so that it can improve environmental aspects when compared to the use of biodiesel without HHO gas.