Noise problem arising from transmission gears of automobiles is well known to be related to the oxidation of gear materials during crburizing and distortion in the subsequent quenching and tempering process. In order to develop new grade steels with minimal internal oxidation layer which has detrimental effects on gear life and noise reduction, the effects of alloying element, Mn, Cr and Si on the internal oxidation behavier during carburization were studied in comparision to the characteristics of internal oxidation for two commmom transmission gear materials, SCM415H, SCR420H. The chemical composition of the new grade is 0,17C -Si$lt;0.13-0.75Mn -1.0Cr -0.40Mo. The hardenability characteristics of new grade steel is equivalent to that of SCM415H and SCr420H and internal oxidation layer depth after case hardening was smaller than those of SCM415H and SCr420H. The depth of internal oxidation layer was decreased with decreasing the amount of Si which has the highest affinity for oxygen.