Acid rain is a problem of increasing agricultural, environmental, and ecological concerns worldwide. At present NO_X emission has exceeded SO₂ in eastern China. The purpose of this study was to investigate the possible effects of simulated acid rain with lower S/N ratio on gas exchange and membrane system of three dominant trees in subtropical forests. One-year-old seedlings of Cinnamomum camphora, Schima superba and Liquidambar formosana were transplanted into pots with the local soil (yellow-red soil) at Tiantong National Station of Forest Ecosystem, Zhejiang Province. The molar ratio of sulfate to nitrate of the simulated acid rain used in our study was 1.58 ∶ 1, similar to the ratio of NO^-₃ and SO^2-₄ in ambient rainfall in Zhejiang. Seedlings were treated with simulated acid rain of pH 2.5 or 3.5, respectively, every other day from April 15 to August 24 in 2009, and local reservoir water of pH 5.0-5.4 as the control. All of the pots were laid in a greenhouse to exclude ambient rainfall. Gas exchange parameters were determined with a Li-6400XT portable photosynthesis system at late July.Photosynthetic pigment contents, membrane penetration and malondialdehyde (MDA) content in leaves were also investigated at the end of the experiment. No significant difference was observed in these parameters with the treatment of pH 3.5 acid rain for all three species, while pH 2.5 treatment altered gas exchange parameters, including net photosynthetic rate (Pn), stomata conductance (Gs), transpiration rate (Tr) and water use efficiency (WUE). The Pn of C. camphora, S. superba and L. formosana under pH 2.5 treatment declined by 16.0%, 31.7% and 15.7%, respectively. Membrane penetration and MDA contents in the seedling leaves of three species were increased significantly. Compared with the controls, the membrane penetration in leaves of C. camphora, S. superba and L. formosana under pH 2.5 treatment were increased by 28.6%, 38.8% and 39.6%, and MDA contents were enhanced by 31.6%, 35.1% and 35.2%, respectively (n=12, P<0.05), suggesting that the decrease of photosynthetic activity was probably caused by non-stomatal factors in combination with stomatal closure. Treated with nitrogen fertilizer, total chlorophyll content of the leaves were increased by 4.0%-29.2%, and net photosynthetic rate on the basis of chlorophyll content declined significantly under pH 2.5 acid rain treatment, ranging from 22.7% to 43.4%, depending on the species. Based on the results, we conclude that acid rain treatments can induce partial closing of stomata, damage membrane system and decrease photosynthetic activity of plants, and lower S/N ratio may mitigate such negative effects compared with the treatment of higher S/N ratio. Furthermore, C. camphora has the best capacity to acclimate to acid rain stress followed by L. formosana and S. superba. This study improves our understandings in effects of acid rain on plant growth under lower S/N ratio.