The heat treatment charaterristic of SCM 440 and B 16 steels has been investigated in various condition(A, B and C) to the effect of heat treatment on mechanical properties, and the following results were obtained 1. We are obtained a good nitriding characteristic in bainitic structure than other heat treatment cycle in our experiment 2. Fatigue characteristic has shown in order of B>C>A condition as heat treatment cycle 3. The effective hardening depth and fatigue characteristic has been excellented in B 16 than SCM 440 after the nitriding and Q. T for B and C condition 4. Nitriding depth has been increased in addition of Cr, V and the nitriding efficiency is increased as easiness of banite formation to wide range of cooling rate by addition of Mo 5. The depth of compound layer in parallel surface, notched slop plane and notched bottom has been varied to the nitriding depth of 5, 4 and 3μ in relatively uniform pattern after 10h nitriding treatment for SCM 440 into A condition