Because of high specific stiffness, the aluminum alloy has been used for various industry field. Specially, the heat-treated aluminum alloy is difficult-to-machine material and machining test is necessary to evaluate and improve the machinability. In order to manufacture the functional part, appropriate cutting condition is selected by considering surface quality, machining time, and workpiece deflection by cutting force. In this investigation, the machinability of A16061-T6 is estimated by changing cutting conditions. The variable cutting conditions are cutting speed, depth of cutting, and feed rate. The estimation is done by analysis of cutting force, surface roughness, and surface shape according to the change of cutting conditions.