In the current work, an experimental investigation was conducted to recommend the optimal concentration of alumina nanoparticles (Al2O3) into Jojoba biodiesel-diesel (JB20D) fuel blend at which the best diesel engine performance and exhaust emissions were attained. The Al2O3 nanoparticles with concentrations varied from 10 to 50 mg/l by step of 10 mg/l were mixed into JB20D fuel blend with the help of ultrasonic stabilization. The results of the present study revealed that JB20D slightly reduced the engine performance and increased its emission characteristics at all engine tested operating conditions as compared to pure diesel oil. Utilizing of Al2O3 additives was found to improve all engine performance characteristics. However, the best emission characteristics were obtained at the dose level of 20 mg/l, where remarkable emissions reduction were observed; NOx by 70%, CO by 80%, UHC by 60%, and Smoke opacity by 35%. While the best of both mechanical performance and engine combustion characteristics were achieved at a concentration of 40 mg/l, where the reduction in the brake specific fuel consumption - bsfc was by 12% and increase in the cylinder peak pressure p(max), the maximum rate of pressure rise - dp/d theta(max), and maximum rate of gross heat release -dQ(g)/d theta(max) were 4.5%, 4%, and 4%, respectively. According to the comparisons of engine performance and emissions, the recommended concentration of Al2O3 in JB20D blends was concluded to be 30 mg/l, which gave remarkable enhancement in all engine performance parameters.