The study investigates the effect of ethanol and Moringa antioxidant on the performance and emission characteristics of a Soybean biodiesel blend (B15, B20, and B25) using a direct injection, four-stroke, naturally aspirated, water-cooled single-cylinder diesel engine equipped with SCADA software. The effect of reaction parameters on FAEE yield such as, time, catalyst concentration, molar ratio of alcohol to oil, and blending quality, was optimized using the one factor at a time experimental technique. The maximum yield of 97.8% biodiesel was produced at the ideal catalyst concentration, blending quality, alcohol to oil molar ratio, and time of 1 h, are 1%, 12:1, and 500 rpm, respectively. The Rancimat method was used to assess the oxidative stability of pure biodiesel after the natural antioxidant (extracted from Moringa leaf) was added at concentrations of 1500, 2500, 3500, and 4500 ppm. The addition of antioxidants to biodiesel significantly increased its induction time from 4.52 to 19.98 h. Brake-thermal efficiency increased by 4.4% whereas brake-specific fuel consumptions decreased by 4.6% for B15E2M (15% SB+2E + M) when compared to B15. Emission characteristics of B25E2M showed higher reduction of CO, HC and NOx by 20.27%, 8% and 7% as compared to the B25 respectively. The physicochemical qualities, performance, and emission characteristics of B15 blends with additive are generally comparable to those of diesel fuel. In conclusion, both additives significantly improved the combustion performance of soybean biodiesel blend.