The renewable energy sources have gained their importance from last few decades. The enhanced environmental concerns & exhaustion of fossil fuels reserves has inspired the researcher to find alternative energy sources. The biodiesel obtained from Vegetable oil & animal fat is recommended for replacement of conventional fuels. The use of Waste Cooking Oil is economical and makes the biodiesel competitive in price with petroleum based fuels. The current study is aimed to study the influence of Aluminium oxide nano additives on the performance and emissions characteristics of compression ignition engine fueled with waste cooking oil bio-diesel. In the experimentation, 50ppm & 100ppm of Aluminium oxide nano-particles were mixed in waste Cooking Oil biodiesel. Experiments were carried out with B20 WCO fuel and adding Aluminium oxide nano particles in the proportion of 50ppm & 100ppm respectively to B20WCO biodiesel blend. The results revealed that, the brake thermal efficiency increased and specific fuel consumption has reduced for B20WCO & B20WCO nano additive blends. When compared with diesel, there is a significant reductions in the parameters like UBHC, NOx and CO emissions at B20WCO in conjunction with 50ppm &100ppm Aluminium oxide nano-additive blends. However, there is a slight increase in NOx emissions for B20WCO & B20WCO nano additive blends.