In this study, Botryococcus braunii algal oil has been converted into methyl ester with the aid of transesterification reaction. The samples B20 were prepared for each methyl ester obtained from Botryococcus braunii algal oil separately and then the cerium oxide nanoparticles were added to each B20 blend sample at they dosages of 50, 75, and 100 ppm with the aid of an ultrasonicator. Moreover, in the absence of any engine modifications, the emission characteristics of those blend samples have been investigated from the experimentally measured engine exhaust emissions of CO, CO2, 02, NO, and UHC. The experimental results reveal that the use of biodiesel blend with nano additives in diesel engine has exhibited a reduction in exhaust emissions.