The effect of aging treatment on the microstructure and corrosion resistance of Mg-4Zn alloy sheets prepared by high strain rate rolling was investigated by optical microscopy（OM），scanning electron microscopy（SEM）， transmission electron microscope（TEM）， static immersion and electrochemical measurement. The results show that the as-rolled Mg-4Zn alloy is composed of fine homogenous dynamic recrystallization grains with the average grain size of 3 μm and many non-uniformly distributed precipitates. Dislocations are observed in some local regions. After pre-aging treatment， a large number of GP I zones（up to about 3~10 nm in length， 2~3 atomic spacing in width） and ball-like GP II zones（up to about 4~10 nm in diameter） are formed in the grains. Dislocation density is significantly reduced， and precipitates are more uniformly distributed in the Mg-4Zn alloy aged at 70 ℃/10 h + 160 ℃/2 h. A combination of filament corrosion and pitting corrosion is the corrosion mode of as-aged Mg-4Zn alloy in Hank's solution. With the prolonged aging time， its corrosion resistance increases at first and then decreases， and the alloy aged at 70 ℃/10 h + 160 ℃/2 h exhibits the best corrosion resistance due to the reduced dislocation density and the uniform distribution of precipitates. The average corrosion rate，the thickness of corrosion film，corrosion potential and corrosion current density are 0.28 mg·cm-2·d-1，6.3 μm，-1.41 V and 11.8 μA/cm2，respectively.