Biodiesel is developed an alternative energy sources. Biodiesel as an alternative fuel oil was already thinning. Growing fuel needs, while oil was very limited. Castor oil has a few drawbacks, namely viscosity and density are high and lower heat value. Some efforts to improve the quality of biodiesel, among others, is to blend the biodiesel with soybean oil which has chemical properties that are better. This research aims to know the influence of the variation of the composition of the mixture against the characteristics of biodiesel and the composition of the mixture that gives the most optimal. This research was conducted on the making of biodiesel blend of castor oil and soybean oil, as well as comparing with the standard SNI 7182-2015. A process through two phases, namely the process of esterification and transesterification was conducted. Esterification process using methanol 22.5% of the volume of oil and acid catalyst homogeneous H2SO4 0.5% by comparison. The process of Transesterification using methanol is 15% of the volume of oil catalyst base homogeneous namely KOH by comparison of 1% of the volume of oil. Biodiesel blending is done with a 60- minute reaction time with a temperature of 60 °C. Comparison of mixed biodiesel with soybeans biodiesel is 0:100,10:90,20:80,30:70,40:60,50:50,60:40,70:30,80:20,90:10:100:0%. The best comparison and optimum obtained on blends of biodiesel with a biodiesel soya distance on the composition of 30:70% (BJBK37) can improve the quality of biodiesel produced including 869.47 kg/m3 density, viscosity 7.1 cSt, and flash point of 189.37 °C, and heat value of 9329.46 CAL/g. Characteristics on the value of viscosity, density, and the resulting heat value still do not meet the standards of the biodiesel SNI 7182-2015.