In this paper, the experimental investigation of the effect of antioxidant additive (A-tocopherol acetate) on oxidation stability and NOx emissions in a methyl ester of neem oil fueled direct injection diesel engine has been reported. The antioxidant additive is mixed in various proportions (100-400 ppm) with methyl ester of neem oil. The oxidation stability was tested in Rancimat apparatus and emissions, performance in a computerized 4-stroke water-cooled single cylinder diesel engine of 3.5 kW rated power. Results show that the antioxidant additive is effective in increasing the oxidation stability and in controlling the NOx emissions of methyl ester of neem oil fueled diesel engines. However, HC, CO, smoke emissions and brake specific energy consumption were found to have increased by the addition of antioxidants. (C) 2014 Elsevier Ltd. All rights reserved.