Oxidation stability and NOX emission characteristics of biodiesel is a challenge to adopt biodiesel as fuel in diesel engine. In this study oxidation stability and emission characteristics of the 20% blend of calophyllum biodiesel with diesel (B20) is investigated with the different proportions of leaf extract additive. The addition of leaf extract as additive in the biodiesel proved improvement in the oxidation stability. The oxidation stability increases with the increase in leaf extract additive proportion. NOX emission for 1.5% of leaf extract additive with B20 (B20A15) reduced 23% at full load. CO and HC emission increases slightly with the increase in additive proportion but it is still lower than that of diesel fuel. (C) 2016 Elsevier Ltd. All rights reserved.