Energy needs of fossil fuels are increasing, causing a reduction in fossil fuels. Needed the development of alternative fuels, which are renewable. Vegetable oil biodiesel is classified as renewable fuel, such as castor oil and palm oil. Vegetable oil has a weakness that is still high viscosity, and for its superiority that is environmentally friendly. To improve the viscosity characteristics, by mixing castor oil and palm oil in the form of oil before the biodiesel process. Raw material for castor oil and palm oil biodiesel has the potential to be very large to be developed into biodiesel fuel. This study aims to determine the effect of mixed reaction time and temperature ratio of 60% castor oil and 40% palm oil on the nature of biodiesel. For the manufacturing process using the esterification stage method by mixing methanol 225 ml and 5 ml sulfuric acid. The transesterification method uses 150 ml methanol and KOH (potassium hydroxide). Mixing between castor oil and palm oil with the influence of temperature variations 600, 900, 1200, and 30 minutes, 60 minutes, 90 minutes. The result of mixing between castor oil and palm oil results in a decrease in density and viscosity, but there is no change in the value that is too significant between samples. Graphs on flash point testing and calorific value increase with the longer heating time.