Abstract: The relation between microstructure and mechanical properties of 102 steel was studied by room temperature tensile strength and hardness test of some 102 steel samples with normal or aging microstructure. The results showed that room temperature tensile strength and hardness of the samples with normal microstructure could reach the standard maximum. Mechanical properties would become lower with the aging of microstructure. When aging achieved the four level, mechanical properties had closed to the standard minimum.