This work is oriented to enhance the diesel engine emissions and performance run with biodiesel from waste cooking oil (WCO) blended with nano cerium oxide. Methyl ester properties were confirmed with ASTM standards. Biodiesel blends were achieved by mixing of 10 and 20% by volume of methyl ester to pure diesel as B10 and B20, respectively. Concentration of 50 ppm nano CeO2 was blended with biodiesel blends as B10C50 and B20C50. The maximum enhancements in thermal efficiencies of B10C50 and B20C50 were 5 and 10 %, respectively about B10 and B20. The highest increases in brake power of blended nano additive were 7.5 and 11% biodiesel were about B10 and B20, respectively. The highest decreases in specific fuel consumptions were 6 and 11%, respectively about biodiesel blends for addition of nano additive. Methyl ester mixtures with nanomaterials achieved the highest declines in CO concentrations by 17 and 22%, respectively related to B10 and B20. The maximum decreases in NOx emissions were 8 and 13% for B10C50 and B20C50, respectively about biodiesel blends. Biodiesel mixture B20 with CeO2 nano additive of 50 ppm concentration was recommended to show the emissions reductions and performance improvement about methyl ester blends.