The purpose of this study, to produce biodiesel from waste oils which are harmful to the environment and human health, and this was to investigate the use of biodiesel as a fuel in internal combustion engines. For this purpose, waste fish oil methyl ester(WFOME) and waste cooking oil methyl ester(WCOME) was produced by transesterification method from waste fish oil and waste cooking oil as an alternative to diesel engine fuel. Then, standard diesel fuel (D2) and two fuels are called as WFB75 and WCB75 obtained by blending the FOME and COME with the D2 with a ratio of 75 % on volume basis were used as fuels in a diesel test engine. After more, methyl esters have been used as fuel in a diesel engine of single-cylinder, four stroke, direct injection and air-cooled; and the effects of fuels on engine performance and exhaust emissions have been comparatively investigated with standard diesel fuel (D2). As a result of the test results obtained from the comparison of results with each other fuels are taken into account, in terms of exhaust emissions of WFB75 and WCB75 fuels were demonstrated better properties than D2 fuel. Exhaust emissions of WFB75 and WCB75 fuels (HC and CO) lower than the emergence of diesel fuel, fuel combustion characteristics of a good and positive effects on the environment taken into consideration, it was concluded that these fuels can be used as an alternative to diesel fuel.