Ten-day-old Zea mays L. Xinyu No.4 seedlings were naturally stressed by stopping irrigation. Water content and water potential in attached leaves were reduced after treatments of 48 and 72h, which repre-sent moderate and severe water stress, respectively. At moderate water stress, the apoproteins of light-har-vesting complex II (LHCII) decreased more rapidly than the content of chlorophyll. However, the con-tents of both chlorophyll and apoproteins decreased markedly in severe water stressed maize leaves. North-ern blotting showed that the loss of apoproteins of LHCII in water stressed maize leaves is partially due to the decline of the steady state level of mRNA for LHCII, which indicated that the expression of LHCII under water stress is regulated at the transcript level. Circular dichroism measurements of LHCII in thyla-koids isolated from water-stressed maize leaves revealed that the LHCII was dissociated and the conforma-tion of LHCII in thylakoids was also altered by water stress.