Effects of alloying elements on microstructure and mechanical properties in conventional microalloyed bainite forging steels were examined. Regression equations of carbon equivalent C_eq and B_s temperature for reheated and continuously cooled bainite steel were obtained. Coefficients of C_eq equation and B_s equation were well correlated. When steels were strengthened to the same extent by alloying elements, microstructures became fine especially by alloying of Cr, Mn, and Mo. Tempering at 473K improved the impact value. It is assumed that termpering at 473K promoted precipitation of supersaturated carbon in bainitic ferrite. Tempering at 573K decreased retained austenite and improved the 0.2% proof stress.