This paper presents new test results of efficiency improvements in a permanent magnet synchronous machine. It has high slot fill aluminum winding so that winding losses can be extremely reduced compared to typical round copper winding. Two test machines with the proposed aluminum winding and the typical copper winding are fabricated. Structures and materials of the stator core, rotor core and rotor permanent magnets are the same. The number of series turns of the winding is also the same. Therefore, their designs of magnetic circuit are the identical so that measured back EMFs and measured torques with respect to currents of the proposed aluminum winding machine are corresponding to that of the copper winding machine. In calculated efficiency maps, it is found that the aluminum winding machine has a notable benefit when the coil temperature rises. In measurements of efficiencies, it is experimentally demonstrated that the proposed aluminum winding machine has high efficiency at low-speed region.