Several motors utilizing the SMC material have been developed. In order that the motor with the SMC core is accepted in the market, the motor efficiency is very important. For higher efficiency, this paper designs a DC motor by using the experimental design method coupled with finite element analysis. First, this paper clarifies the efficiency of the DC motor using the developed SMC core, and compares with a motor made of the conventional laminated core. Next, in order to improve the motor efficiency, eight parameters are optimized by using the experimental design method. The highest efficiency of the optimized motor is improved from 53.7% to 68.9%, that is, the improvement of 15.2%.