The experimental study was conducted to investigate the effect of using Cresson oil biodiesel on CI engine emissions and performance. This research aimed to examine how using innovative biodiesel blend formulations made from Cresson oil affected the performance and emissions of CI engines. The proportion of Cresson oil biodiesel added to conventional Iraqi diesel fuel into volume ratios of 10%, 20%, 40%,60%,80%, and 100 %. The engine compression ratio was set to 18, and the fuel injection timing was set at 23º bTDC. The Experiments show that this biodiesel reduces the engine's thermal efficiency, heat release, delay time, and cylinder pressure while increasing the exhaust temperature (EGT) and brake-specific fuel consumption (BSFC). There has been an increase in emissions of nitrogen oxides (NOX) and carbon dioxide (CO2), but a reduction in emissions of carbon monoxide (CO), soot, and unburned hydrocarbons (HC).