The ever increase in global energy demand, consumption of depletable fossil fuels, exhaust emissions and global warming, all these led to search about alternative fuels. Biodiesel and its blends with diesel fuel are investigated to solve the problem of depletion of fossil fuels and environmental impact. Biodiesel was produced from waste cooking-oil by transesterification process. Blends of waste cooking-oil biodiesel and diesel oil were prepared in volume percentages of 20, 40, 60, 80 and 100% as B20, B40, B60, B80 and B100. Biodiesel blends have ASTM standards of physical and chemical characterization near to diesel fuel. Diesel engine performance and exhaust emissions were studied experimentally for burning waste cooking-oil blend with diesel fuel. This experimental was applied on a diesel engine at different engine loads from zero to full load. Thermal efficiencies for waste cooking-oil biodiesel blends were lower than diesel oil. Specific fuel consumptions of biodiesel blends were higher than diesel fuel. Higher exhaust gas temperatures were recorded for biodiesel blends compared to diesel oil. CO2 emissions for waste cooking-oil biodiesel blends were higher than diesel oil. CO and HC emissions for biodiesel blends were lower than diesel fuel. NOx emissions for biodiesel blends were higher than diesel fuel.