Waste cooking oil methyl ester (WCO-ME) is produced by the transesterification of waste cooking oil (WCO) on laboratory scale setup and it can be used as a biodiesel in stationary diesel engine. The proceeding study investigates the effect of biodiesel and its blends varying from B10 to B80 on the engine performance, emission and combustion characteristics. The properties of diesel and biodiesel are examined and compared. The experimental results show that the use of WCO-ME in an unmodified direct injection diesel engine has yielded higher brake specific fuel consumption (BSFC) due to low calorific value. It is also observed that at full load the brake specific energy consumption of biodiesel blends are higher than that of diesel. Further, biodiesel blends show a reduction in emission properties such as carbon monoxide (CO), carbon dioxide (CO₂), unburnt hydrocarbon (UHC) and smoke opacity with slight increase in nitric oxide (NO) emission compared to diesel at full load. Overall combustion characteristics for all blends are found to be quite similar to that of diesel. Hence, the WCO-ME is a promising diesel fuel substitute that can be produced by recycling waste cooking oil without any engine modification and furthermore, becoming less dependent on fossil oil imports thereby decreasing the environmental pollution.