In this study, the effect of tempering treatment on the mechanical properties in modified 440A steel has been investigated. The amount of remaining carbide decreased with increasing the austenitizing treatment temperature, and all carbides were completely dissolved at $1250^{circ}C$. The amount of remaining carbide decreased with increasing the time of austenitizing, but the carbide remained insoluble up to 120 minutes at $1050^{circ}C$. With increasing the tempering temperature, tensile strength decreased, and elongation increased slowly, while hardness rapidly decreased, and impact value unchanged and then rapidly increased over $500^{circ}C$. The strength and hardness slowly decreased, while the elongation and impact absorbed energy increased with increasing the tempering time. $Cr_{23}C_6$ type carbide was precipitated and sharp decrease of elongation and toughness by tempering did not appear.