The wear behavior and mild-severe (M-S) wear transition of Mg-10Gd-1.5Y-0.4Zr alloy were investigated within a temperature range of 20-200 °C. The morphologies and compositions of worn surfaces were examined to identify the wear mechanisms using scanning electron microscope and energy dispersive X-ray spectrometer. The microstructure and hardness in the subsurfaces were analyzed to reveal the M-S wear transition mechanism. Under a constant loads of 20, 35 and 40 N, each wear rate-test temperature curve presented a turning point which corresponded to the M-S wear transition. In mild wear, the surface material was plastically deformed and hence was strain- hardened, whereas in severe wear, the surface material was dynamically recrystallized and consequently was softened. It has been found that the critical temperature for M-S wear transition decreases with increasing the normal load, and the normal load exhibits an almost linear relationship with critical temperature for M-S wear transition. This work reveals that the M-S wear transition of the studied alloy conforms to the surface DRX temperature criterion.