The effect of quenching rate on the exfoliation corrosion of Al-5Zn-3Mg-1Cu aluminum alloy thick plate was investigated by means of end-quench technique, corrosion immersion test, optical microscopy, transmission electron microscopy and scanning and transmission electron microscopy. The resistance to the exfoliation corrosion of Al-5Zn-3Mg-1Cu aluminum alloy thick plate decreases with the decrease of quenching rate (from 2 160 ℃/min to 100 ℃/min), and exfoliation corrosion rate is from P to ED with the maximum corrosion depth increasing from 15μm to 530μm. The decrease of quenching rate leads to a larger amount of second phase particles at grain boundaries, a higher concentration of Zn and Mg in them and wider precipitate free zone near grain boundaries, which was the main reasons for lower resistance to exfoliation corrosion.