The need for fossil fuels continues to increase, while the supply of fossil fuels is depleting. Then alternative energy is needed as a substitute for fossil fuels, one of which is biodiesel. Biodiesel is an oil fuel obtained from vegetable oil through a transesterification process. To improve the characteristics of biodiesel from vegetable oils, one way that can be done is by mixing vegetable oil with other vegetable oils. The research aims to determine the effect of the composition of a mixture of castor oil and palm oil against the properties of biodiesel (density, viscosity, flash point and calorific value). The process of making biodiesel is carried out with mixed variations of 100: 0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90, 0: 100 (%). In the manufacturing process through the esterification process using homogeneous acid catalyst (H2SO4) and the transesterification process using a homogeneous base catalyst (KOH), with a reaction time of 60 minutes and a temperature of 65⁰C. The results showed that the value of the density, viscosity and flash point test parameters tended to decrease along with the increase in the composition of the mixture of palm oil to the mixture composition, but with the increasing composition of the mixture of palm oil to the mixture composition, the resulting heating value tends to increase. The optimal variation of the composition of biodiesel, a mixture of castor oil and palm oil with density, viscosity, flash point and calorific value parameters meet the SNI 7218-2015 standard, which is in the composition 60:40 (%).