Energy has an important role that can not be separated from human life. Dependence excessively on non-renewable energy can lead to energy crisis problems. To reduce dependence on non-renewable energy, it needs an alternative substitute which on of them is biodiesel. Biodiesel is one of the most suitable alternative fuels to be developed in Indonesia, because of the abundance of natural resource owned. Vegetable oils that are prospectively developed as raw materials for biodiesel include castor oil and virgin coconut oil. This study aims to determine the effect of variations in the composition of the mixture on characteristic of biodiesel and the composition of the mixture which gives the most optimal quality. In the process both of the oil through two stages of the esterification and transesterifications process. The process of esterification using homogeneous acid catalyst (H2SO4) with 60-minute reaction time with a temperature of 80°C, and the process of Transesterification using homogenized base catalysts (KOH), with a 60-minute reaction time with a temperature of 60°C. From the data of this study the result can be concluded that the value of density, viscosity, and flash point tends to decline along with increasing the composition of coconut oil. However, it is inversely proportional to the calorific value that increases with the increasing of coconut oil composition. The composition of the mixture of castor oil and coconut oil that provides the most optimal quality the composition of a mixture of castor oil 10%:90% coconut oil. The resulting characteristics such as the density of 852,886 kg/m³, the viscosity of 5,9 cSt, and a flash point of 117.45°C. But in contrast to the calorific value produced has a value higher than the other composition variations of 9064.68 kal/g. The resulting bodiesel characteristics meet the standards established in SNI 7182-2016 or ASTM D6751.