Effects of strain hardening exponents on the retardation behavior of fatigue crack propagation are experimentally investigated. The retardation of fatigue crack propagation seems to be induced by the crack closure at crack tip. The phenomenon of crack closure becomes remarkable with the increment of strain hardening exponent and magnitude of percent peak load. Thie ratio of crack growth increment(a_d/W_d) is influenced by a single overloading (a_d) and estimated plastic zone size (W_d=2r_y) is increased according with the increasing of strain hardening exponents. The number of retarded crack growth eycles were (N-d) decreased as the baseline stress intensity factor range: (△K_b) was increased. Within the limitation of these experimental results obtained under the single overload, an empirical relation between crack retardation ratio (Nd/N^* ), strain hardening exponent (n) and percent peak load (%PL) has been proposed as ; Nd/N^* = exp [PL·{PL·A(n)+B(n)}] where, A(n)=αn+β,B(n)=γn+δ, B(n)=αn+δ, PL=%PL/100 and α=0.78, β=0.54, γ=0.58 and δ=-0.01, It is interesting to note that all these constants are identical for materials such as aluminum(A3203), steel(S45C), steel(SS41) and stainless steell(SUS316) used in this experimental study