Microstructural examinations of T6-treated WE54 magnesium alloy were conducted after different aging conditions, and the influence of aging on electrochemical behavior of this alloy was investigated. For three batches of samples, with increasing aging time, the amount of precipitate phases was greatly promoted, and they formed in a strengthening continuous way. Electrochemical study showed that the value of corrosion potential followed the tendency to decrease when the aging condition transformed from under-aged to peak-aged. However, after peak-aging, the corrosion potential was raised to higher values. Explanations for the observed phenomena were based on the relationship between microstructure, especially precipitate phases, and electrochemical behavior. At under-aged condition, matrix served as galvanic cathode and precipitates acted as galvanic anode. Because the amount of precipitate would rise with prolonging aging time, it is natural that corrosion potential decreased. For over-aged alloys, metastable precipitate phases might in situ change to equilibrium phases, rendering increase of corrosion potential possible.