Energy needs in Indonesia is increasing every year, but the energy seserves are running low. Biodiesel belongs to renewable natural fuel because its raw materials come from natural materials that can be renerated quickly and do not require a very long time, therefore castor oil and corn oil have potential to become the alternative energy to substitute fossil fuel. The process of preparation by means of Esterification between fatty acids and alcohols used acids and alcohols used acid catalyst, and then glycerine separation was done to reduce the viscosity by transesterification reaction. The purpose of this research is to obtain the result about the effect of time and temperature of mixing castor oil and corn oil to its density, flash point, calorific value and viscosity. In the process both oils are mixed with various temperature 60ºC, 90ºC and 120ºC with eachone varied again with heating time 30, 60 and 90 minutes. Thereafter, an Esterification process with an acid catalyst converts FFA to an alkyl ester with a reaction time of 60 minutes at a temperature of 60º C. The Esterification generally uses a homogeneous acid catalyst such as sulffic acid (H2S04), followed by a Transesterification process using a homogeneous base catalyst (KOH), with a reaction time of 60 minutes at temperature 60º C. Then the results of biodiesel was tested to see its density, viscosity, flash point and calorific value. From the research data, it can be concluded that the composition of biodiesel mixture of castor oil and corn oil that meets the standard was on the sample with 90ºC 30 minutes, 90ºC 60 minutes, 90ºC 90 minutes, 120ºC 30 minutes, 120º60M, 120º90M, where the characteristic of biodiesel such a density, viscosity, flash point and calorific value are in accordance with SNI 7182-2015, whereas in the sample with 60ºC 30 minutes, 60ºC 60 minutes and 60ºC 90 minutes for only viscosity value that has not complied with SNI standard.