The shortcomings of fossil fuels and the Earth's increasing temperature haveaised researchers' interest in alternative fuels for use in automobiles. In this study, biodiesel blends containing 20%, 40% and 60% soybean oil-basedbiodiesel (B20 and B40) along with cerium oxide (CeO2) at concentrations of30, 60, and 90 ppm (denoted as C30, C60, C90) were added to pure diesel. The resulting blends were labelled as B20C30WOE,B20C60WOE,B20C90WOE, B20C30WE, B20C60WE, B20C90WE for B20, and similarly for B40, B60 and D100, with and without exhaust gasrecirculation (EGR) (denoted as WOE and WE). The selection of cerium oxide and soybeanbiodiesel was based on their excellent thermophysical properties. Theexperimental trials were conducted on a constant speed and compression ratio of 18 in a CI engine for all the blends mentioned earlier, at variable loads of 0%, 25%, 50%, 75%, and 100%. The study focused on evaluating theperformance and emission parameters. The brake thermal efficiency of B60C60WE is 39.26% higher and of B60C90WOE is 21.67% higher when comparing with and without EGR. This shows that as the concentration of cerium oxide increases at higher (100%) load, the thermal performance improves with EGR compared to pure diesel (D100). The lowest brakespecific fuel consumption (BSFC) was observed for B60C60WE at full load in comparison to diesel. The different exhaust gases were analyzed by an AVLgas analyzer, and it was observed that the addition of cerium oxide mixed insoybean oil helps to minimize emissions such as HC, CO, CO2, and NOx in biodiesel blends compared to pure diesel. This improvement is due to thecombined effect of oxidation and the thermal properties of cerium oxide.