The low cycle fatigue (LCF) behavior of high-strength structural steel under biased strain control has been investigated. Seven strain ratios with constant maximum strain amplitude were adopted. Significant cyclic softening and mean stress relaxation were observed in all cases. The fatigue life under biased strain control could be well predicted by Coffin-Manson relationship. Fractography by scanning electron microscopy was used to determine the LCF failure mechanisms and fatigue crack propagation modes.