The low cycle fatigue(LCF)properties of as-extruded AZ31 Mg alloy were investigated under total strain amplitudes in the range of 0.4%-1.2%with strain rate of 1×10- 2s -1.Due to the twinning effect in compression during loading and the detwinning effect during unloading,the alloy showed an asymmetric hysteresis loop.The cyclic stress response exhibited cyclic hardening at high total strain amplitudes.The cyclic deformation behaviors were discussed using the Coffin-Manson plot,which divided the plastic strain amplitudes into the tension side and the compression side.Through the LCF tests that were started from either tension or compression under a total strain amplitude of 1.0%,the interaction between the twinning effect and dislocation was analyzed.The twinning effect during the LCF test and the variation of the dislocation density were investigated using optical microscopy and transmission electron microscopy,respectively. The low cycle fatigue (LCF) properties of as-extruded AZ31 Mg alloy were investigated under total strain amplitudes in the range of 0.4% -1.2% with strain rate of 1 × 10-2 s -1. To the twinning effect in compression during loading and the detwinning effect during unloading, the alloy showed an asymmetric hysteresis loop. The cyclic stress response exhibited cyclic cyclic at high total strain amplitudes. The cyclic deformation behaviors were discussed using the Coffin-Manson plot, which divided the plastic strain amplitudes into the tension side and the compression side. Through the LCF tests that were started from either tension or compression under a total strain amplitude of 1.0%, the interaction between the twinning effect and dislocation was analyzed. The twinning effect during the LCF test and the variation of the dislocation density were investigated using optical microscopy and transmission electron microscopy, respectively.