Waste cooking oil as an alternative fuel in oil burners allow facing the challenges of rising diesel oil prices, reducing gradual depletion of fossil fuel, saving imported fuel from abroad with foreign currency and reduction of exhaust emissions that cause global warming. Waste cooking oil was preheated to 90 ℃. Properties of waste cooking oil were near to diesel fuel.This paper proposes to investigate the combustion characteristics of waste cooking-diesel oil blends at constant heat load. Waste cooking-diesel oils blends were prepared by volume percentages of 0, 20, 40, 60, 80 and 100%.Exhaust gas temperature, axial inflame, radial inflames temperatures, exhaust emissions and combustor were investigated for waste cooking-diesel oils blends in swirled oil burner.The experimental results showed that WCO-LDO blends emitted lower emission and values compared to diesel oil. Hydrocarbons emissions for waste cooking-diesel oils blends were higher than diesel oil. Increases of radial inflame temperature of waste cooking-diesel oils blends compared to diesel oil. NOx emissions of for LDO was higher than any waste cooking-diesel blend. The percentage of heat transferred to the combustor wall decreased for WCO-LDO blends compared to LDO.Waste cooking diesel oil blends can be used as an alternative fuel oilsin oil burner.