Seedlings of seventeen tree species were fumigated with 600, 1,000, and 2,000 ppb of sulfur dioxide (SO2), respectively, for 48 hours. Foliar injury symptoms and several physiological activities of each species were measured for determining the susceptibility to SO2. After being fumigated with 600 ppb of SO2, no foliar injury symptoms occurred for all species. However, chlorophyll fluorescence (Fv/Fm ratio) of two species reduced to below 7.5 and net photosynthetic rates of sixteen species decreased significantly. When increasing SO2 concentration to 1,000 ppb, reddish-brown interveinal chlorosis was observed in most species and white or ashen chlorosis shown in Melia azedarach and Koelreuteria henryi. Under this treatment, Fv/Fm ratio of twelve species reduced to below 7.5 and all seventeen species showed significant reduction in the net photosynthetic rates. The Fv/Fm ratio of both Delonix regia and Lagerstroemia speciosa were below 0.1. In addition, their net photosynthetic rates and those of M. azedarach and K. henryi were all reduced to 4-13% of before fumigation, indicating that the physiological activities of these four species were greatly inhibited. When fumigated with 2,000 ppb of SO2, leaves of D. regia, L. speciosa and Michelia compressa were severely injured and all fell off, while leaves of the other fourteen species did not fall off but all showed various degrees of foliar injury. In this study, net photosynthetic rates, stomatal conductance, and the Fv/Fm ratio of all species were significantly reduced. However, the chlorophyll concentrations of ten species were not significantly reduced after treatment, indicating that SO2 did not severely injure the foliar chlorophyll of these species. Results showed that Liquidambar formosana, Nageia nagi, Diospyros maritime, Pistacia chinensis, Terminalia catappa, Machilus zuihoensis, and Aglaia formosana were the most tolerant species to SO2. On the other hand, D. regia and L. speciosa were very susceptible to short-term fumigation with SO2. Photosynthetic rates of all species were found very sensitive to SO2 treatments. Therefore, it can serve as a physiological indicator of susceptibility in seedling of tree species to SO2 stress.