This research investigates the mechanical properties of a Cr-Ni-Mo-alloyed rock drill steel tempered at different temperatures from 150 to 550 C. The highest strength, hardness, and impact energy occur when the steel is tempered at 180 C. Strength, hardness, and impact energy decrease with increasing tempering temperature from 180 to 400 C. For tempering temperatures higher than 400 C, the steel exhibits: 1) an increase in impact energy; 2) an increase in strength and hardness when tempered at 420, 450, and 480 C; and 3) a gradual decrease in strength and hardness when tempered at temperature higher than 480 C. The mechanism of the changes of impact energy and hardness with tempering temperature is proposed.