In our previous paper, assuming that phenomenon of fatigue crack propagation is continuous fatigue crack initiation at crack tip and crack initiation a life is used up when damage caused by cyclic strain near crack tip is accumulated and reached to a certain critical value during Δ N cycles, authors proposed a law- on the fatigue crack propagation rate under fully reversed loading neglecting the crack closure phenomenon. In this report, effect of mean stress on the fatigue crack propagation is discussed quantitatively. It is assumed that main factors of mean stress which affect the crack propagation rate are phenomena of cyclic creep and crack closure, and a new law on the crack propaga-tion rate is proposed. In order to prove the validity of the law, crack propagation rate curve calculated by the law were compared with experimental results obtained by several investigaters and fairly good agreements between them were found.