The effect of fuel variability in Thailand is that diesel fuel is one of the fuels affected by fuel variability. The use of alternative energy is an alternative to diesel engines. Therefore, this research is interested in studying the physicochemical properties of test fuels, engine efficiency, combustion characteristics, and engine-out emissions of the engine in order to evaluate the production of biodiesel from different feedstocks as an alternative fuel in a single-cylinder diesel engine. Biodiesels produced from castor oil and pork lard oil by transesterification process with methanol using potassium hydroxide (KOH) catalyst. The fatty acids of biodiesel produced from castor oil (COME) and pork lard oil (PLOME) were characterized by Gas Chromatography-Mass Spectrometer (GC-MS) techniques. It can be seen that the main fatty acids in COME and PLOME are ricinoleic acid (C18:1 OH) and oleic acid (C18:1), respectively. The test fuel properties were examined according to the international fuel standards. The results indicated that the fuel properties of COME and PLOME are well-accepted biodiesel standards and testing methods except in the case of the kinematic viscosity of COME. The engine was operated at a fixed speed of 1,500 rpm with variation in load conditions. The experimental results of the engine performance showed that the use of COME and PLOME had higher brake specific fuel consumption (BSFC) and lower brake thermal efficiency (BTE) compared to diesel fuel. The combustion of COME and PLOME increased CO, HC and smoke emissions while decreasing NOX emissions in comparison with diesel fuel. Consequently, biodiesel derived from castor oil and pork lard oil is not recommended for use as a pure component in the diesel engine, while the use of such biodiesels as a blend component with diesel fuel can be a feasible way to alleviate the current fuel price crisis, which is intensely dependent on oil imports.