A thermo-mechanical treatment process using resistance heating was developed to improve mechanical properties of heat treatable aluminum alloy sheets. In this process, the solutionized aluminum alloy sheets are rolled at room temperature, and then are heat-treated by combination of rapid resistance heating and water quenching to solutionize the sheet without the growth of grains. The process was applied to Al–0.60 mass%Si–0.74 mass%Mg alloy (A6061) sheet to confirm the effectiveness of the process. The sheet reduced from 5 mm to 0.5 mm by multi-pass rolling was resistance-heated up to 893 K in a very short time of 2 s, and immediately water-quenched. The grain of the sheet produced by the present process were reduced to about half of the conventional ones. This led to an improvement of the mechanical properties, i.e. the Vickers hardness and the limiting drawing ratio were increased by 10% and 5%, respectively. It was found that the present thermo-mechanical treatment process is effective in improving the mechanical properties.