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Effect of mean stress on the cyclic stress-strain response, fatigue life, short crack growth and crack initiation of austenitic-ferritic duplex steel has been studied. Cycling with mean stress results in mean strain relaxation and more pronounced initial cyclic softening that does not saturate as in symmetric loading. The mean strain relaxation results in hardening and for high mean stresses long-term cyclic hardening follows. Short crack growth is characterized by crack linkage. The kinetics of short crack growth is similar for symmetric loading and loading with mean stress. The concept of equivalent crack was used to describe the crack growth. The presence of mean stress accelerates crack initiation, which contributes to the decrease of the fatigue life.