The effects of lubricating oil on surface quality of the extruded aluminum product were investigated by carrying out a series of plane strain cold extrusion experiments. The forming dies of extrusion apparatus were assembled with a combination of the taper die and the plane plate tool with the micro-groove arrays formed on its surface. Four lubricants were tested by using the above apparatus. Then, adhesion of aluminum billet to the surface section of the plane plate tool on which the micro-groove arrays were formed, surface roughness of the billet after passing through the above section of the plane plate tool and surface conditions of the billet and tool at the die bearing section of a tool were investigated, and performance evaluation of lubricant for producing smooth surface product could be carried out successfully.