Abstract: The wear behavior of Mg-3Al-0.4Si alloy at wear temperatures of 20~200 ℃ was investigated using a pin-on-disc type wear machine, in which the effects of applied load and temperature on the wear rate were presented. The morphologies of worn surfaces were observed using scanning electron microscope to determine the wear mechanisms involved. Microstructural evolution and hardness change in the subsurface were also analyzed using optical microscope and microhardness tester, respectively. The results show that as temperature increased, the increasing trend for wear rate with applied load was increasingly distinct. The wear behavior of Mg-3Al-0.4Si alloy was classified into the mild wear and severe wear, and increasing temperature decreased the mild-severe wear transition load. The changes of microstructure and hardness in subsurface before and after mild-severe wear transition identified the origin of mild to severe wear transition as the frictional-heating induced dynamically recrystallization (DRX) microstructure transformation and consequent softening effect in the surface layer of pin samples.