As the price of petroleum oil is increasing rapidly day by day. It is necessary to develop a substitute of petro-diesel fuel. An alternate fuel should be economically attractive in order to compete with currently used conventional diesel fuels. Biodiesel is a clean burning diesel alternative and has attractive many features including renewability, biodegradability, and non toxicity and comparable performance. The aim of the present study is to investigate the performance parameters of diesel engine operating on waste frying oil methyl ester (WFOME) and waste frying oil ethyl ester (WFOEE) when these are used as a fuel in diesel engine and then compared with the diesel fuel. It is investigated that the Brake Specific Energy Consumption (BSEC) of WFOME is increased by approximately 8% and Brake Thermal Efficiency (BTE) is decreased by around 7.6% at 50% load while the BSEC of WFOEE is increased by approximately 10.3% and BTE is decreased by around 9.3% than that of diesel fuel when the 100% (neat) WFOME __ampersandsign WFOEE are used in diesel engine. As the blends are increased for the same load, engine consumed the more fuel consumption as compared to diesel fuel. When the 100% WFOME __ampersandsign WFOEE are used in CI (Compression Ignition) engine, WFOME __ampersandsign WFOEE consumed higher fuel in comparison to conventional diesel. The result showed that the neat WFOME and WFOEE when used in diesel engine WFOEE consumed approximately 3% higher fuel in comparison to WFOME at 50% engine load. In general, the physical and chemical properties and performance of ethyl esters are comparable to those of the methyl esters. Methyl and ethyl esters have almost the same heat content. The viscosity of ethyl esters is slightly higher while cloud and pour points are slightly lower than those of methyl esters. The engine tests demonstrated that methyl esters produced slightly higher brake thermal efficiency than ethyl esters. The ethyl ester consumed slightly less fuel as compared to methyl ester.