Research on renewable fuel energy sources and the use of catalysts in increasing their production has always been an interesting topic in this era towards industry 5.0. This is because the world's energy needs are always increasing every year, especially during the industrial revolution. It requires more sources and other types of energy to convert. Based on that need, alternative energy sources that are renewable and abundant were always needed. One form of renewable alternative energy source is biodiesel. Biodiesel is environmentally friendly, clean, biodegradable, and produces low exhaust emissions. One of the raw materials for biodiesel can be obtained from Kepuh seeds (Sterculia foetida). The manufacture of biodiesel goes through five stages, namely pressing, degumming, esterification, transesterification, and purification. Then, the biodiesel that has been produced is added to bio solar in a ratio of 8:2 (biodiesel: bio solar). Additions were made to five samples of the fuel mixture based on the amount of catalyst used (0.8; 0.9; 1.0; 1.1; 1.2%). Based on the results of the biodiesel quality test, the average value for the density test was 0.85 kg/m3, the viscosity was 3.24 CST and the calorific value was 11,090 cal/gram.