Biodiesel is an emperature fuel that is suitable for development in Indonesia, given the abundance of natural resources available. One way to make biodiesel is by mixing castor oil and coconut oil in the form of pure oil through a process of direct mixing with mixed variations according to the specified. Based on the description above, it is necessary to do related research to determine the effect of the composition of the mixture of castor oil and coconut oil on the nature of the oil mixture. In this study, the production of biodiesel from castor oil (was carried outCastor oil) and coconut oil (Coconut Oil). The mixing of the two oils was carried out on the 80°C reaction emperature with a reaction time of 90 minutes to determine the effect of the mixture between castor oil and coconut oil on the nature of the oil mixture as fuel with a ratio of castor oil and coconut oil which is 100: 0, 90:10 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90, 0: 100 (%). The best oil mixture is obtained from the comparison between castor oil and coconut oil on the composition of 10:90(%) which has a significant effect on the characteristics produced including density, viscosity and flash the point obtained is the lowest among other compositions. But different from the value heat that gets the highest value among other compositions is equal to 8763,236 Cal/g.