In this research we investigate the physicochemical characteristics of sweet diesel after desulphurization alone and also these characteristics are tested with the adding of high purity HPLC ethanol (99.9%). Those fuel properties of ethanol blended with diesel were experimentally determined to find their stability and to increase their properties and efficiency in the diesel engines. The physicochemical characteristics of the diesel ethanol blends were determined by the following experiments (cetane number, ASTM distillation, flash point, pour point, kinematic viscosity, ASTM density and calorific value).the aim of this research is to obtain an optimum blend of diesel ethanol fuel to help in improving the diesel engines and to lower the emission in the engine and the exhaust gases produced in the engines. the aim of this research is to obtain an optimum blend of diesel ethanol fuel to help in improving the diesel engines and to lower the emission in the engine and the exhaust gases produced in the engines, and also to help to make an economic improvement in the industry of diesel in Egypt and worldwide.