In this study, Waste cooking oil (WCO) biodiesel with Butylated hydroxytoluene (BHT) and n-butanol additive was used in a diesel engine and its effects on engine performance and exhaust emissions were studied. The biodiesel produced from waste cooking oil by transesterification process, Methanol, sulphuric acid (H2SO4) and sodium hydroxide (NaOH) catalyst were used in the reaction. Engine performance test were conducted with blends (BO, B20, B30, B40, and B100) and the results showed that, B30 is the superior blend among other biodiesel blends. Further to improve the performance characteristics of B30, antioxidants of BHT 2000 ppm and n-butanol 20% by volume was added in the B30 blend. The results of BSFC for the B30 + BHT is 7.3% higher whereas the BTE is 4.6% lower than diesel due to the lower heating value of biodiesel. The heat release rate of B20, B40 and B30 + BHT are almost synchronous to diesel fuel, alongside at higher loads B30+n-butanol shows 37.5% less CO emission and 9% higher NOx emission was observed when compared to diesel fuel. WCO bio diesel and its blends with BHT and nbutanol can be used as a fuel in diesel engine. (C) 2017 Elsevier Ltd. All rights reserved.