Significant population and automobile expansion have resulted in a rapid rise in energy demand. Because of the high demand for energy and the rapid depletion of fossil fuels, experts are concentrating their efforts on developing a suitable alternative fuel for diesel. The performance and emission characteristics of biodiesel made from watermelon methyl ester were investigated using a lanthanum oxide (La2O3) nanoparticle addition. Through the transesterification meth od, biodiesel was produced from non-edible watermelon seed oil. Compared to B20, addition of 100 parts per million (ppm) of La2O3 nanoparticles to biodiesel emulsion fuel reduces CO and HC emissions by 4.75% and 6.67%, respectively. Compared to B20 at full load circumstances, the inclusion of La2O3 nanoparticles at 100 ppm enhances the brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) by 2% and 8.8%, respectively.