This study scrutinizes the influence of amine and biological antioxidants on reduction of NOx emissions in a diesel engine fueled with B100 (100vol.% mango seed methyl ester) and B20 (20 vol.% mango seed methyl ester and 80 vol.% diesel fuel blend). Three amine antioxidants, p-phenylenediamine (PPD), Ethylendiamine (EDA) and N,N’-diphenyl- 1,4-phenylenediamine (DPPD) and three biological antioxidants, dichloromethane (DCM), alpha tocopherol acetate (α-T) and L-ascorbic acid (L-asc.acid) are tested in a kirloskar-make single cylinder four-stroke water cooled diesel engine of 5.9 KW rated power. There are five concentrations used in the antioxidant mixture of biodiesel blends. i.e., 0.005%-m, 0.010%-m, 0.025%-m, 0.05%-m and 0.1%-m. Where, %-m is the molar concentration employed in the antioxidant mixture. Results show that consequential reduction in NOx could be acquired by the accession of antioxidant additive DPPD with the 0.025% concentration from B20 fuel by 15.4% and B100 fuel by 39%. The DPPD additive increased the CO emissions over 7.42% for B100 fuel and 6.44% for B20 fuel. The biological antioxidant DCM exhibits 0.235 g/kWhr for B100 fuel and 0.297 g/kWhr for B20 fuel. Smoke emission is found to have increased with the addition of antioxidants. Slight increase in brake thermal efficiency (0.91%) is accomplished with the addition of antioxidants at full load. The experimental results are compared with analysis of variance and the result is merely the same as to that of experimentation.