Abstract: The effects of drought stress on leaf gas exchange parameters of four greening seedlings，including Syzygium hainanense，Phoebe sheareri，Ilex rotunda，Ficus microcarpa，were studied. The results were as follow： The parameters of net photosynthetic rate（ Pn），stomatal conductance（ Gs） and transpiration rate（ Tr） of the four seedlings continuously decreased greatly with drought time increasing. After 4 days of rehydration，the four parameters increased greatly and still lower than the control level. The Pn and intercellular carbon dioxide concentration（ Ci） of four seedlings greatly decreased with drought time，whereas the value of stomatal limits（Ls） increased gradually. The water use efficiency（ WUE） of I. rotunda and F. microcarpa continuously decreased with drought time increasing， whereas that of R. sinica and C. diplopetela increased initially and then decreased. After 4 days of rehydration， except F. microcarpa，the WUE of the other seedlings returned the control level. The drought resistance of the four seedlings was evaluated by using principal component analysis，and the order of drought resistance was I. rotunda > F. microcarpa > P. sheareri > S. hainanense.