This work investigates the effect of using Bi2O3 nanoparticles at a different proportion of Azolla algae methyl ester in a four-stroke single cylinder diesel engine. Azolla algae can be used to produce biodiesel, because of high oil content. Biodiesel is developed by the transesterification of oil. In the present study, the Bi2O3 nano additives into the oil-based methyl ester blend and its diesel blends are analyzed the emission characteristic at different load. Addition of Bi2O3 nanoparticle is a strategy to reduce emission (CO, HC and smoke) of the biodiesel.