This study reports the potential of Cerium oxide (CeO2) nanoparticles synthesized from Jatropha curcus leaves and Insulin plant extracts to use as a doping constituent with diesel fuel. Investigations were carried out to analyze the effect of cerium oxide nanoparticles on engine performance and smoke emission characteristics. X‐ray diffraction study witness the presence of Cerium oxide in the plant extracts and the average crystal size of CeO2 nanoparticles synthesized from J. curcus leaves and insulin plant extracts was 5 and 25 nm, respectively. Experimental runs were carried out on a 4 stroke direct injection VCR diesel engines at two different compression ratios. The result showed that the brake thermal efficiency is increased by a maximum of 5.5% for 25 ppm CeO2 extract blend from insulin plant with diesel fuel. CO and HC emissions of CeO2 doped diesel blends are lowered by up to 38 and 40% at full load conditions in line with neat diesel and also presents significant results in emission characteristics. Finally, it is worth stating that doping of 25 ppm CeO2 nanoparticles from insulin extracts with diesel at compression ratio of 16 can establish better results than diesel.