Resistance physiological indexes such as soluble proteins(SP),soluble sugars(SS),free proline(Pro),superoxide dismutase (SOD),peroxidase (POD),catalase (CAT) and malondialdehyde (MDA) of four species of samplings:Eucalyptus grandis (Eg),Cinnamomum pedunculatum (Cp),Simmondisa chinensis (Sc) and Camellia sinensis (Cs) were measured after fumigation of different levels of SO₂ in sealed environmental control chambers.Four levels of SO₂ treatments:control (natural concentration),M1 (0.5 mg·L^-1),M2 (1.5 mg·L^-1),and M3 (3.0 mg·L^-1) were set in the present study.The results showed that:(1)The order of the extent of injury of SO₂ on leaves is:Cp2 treatment significantly increased the concentrations of SP,SS,and Pro in leaves of Eg and Sc.There was no significant effect of SO₂ stress on SP and SS of Cp.The stimulated effect of SO₂ stress on Pro of Cp appeared only on 30 d of treatment.The responses of SS (no obvious effect),SP (significant depress effect),and Pro (significant stimulate effect) of Cs to SO₂ stress were different.(3)On the whole,SO₂ stress significantly increased the activities of antioxidant system enzymes (SOD,POD and CAT),and the content of MDA in leaves of Eg and Cp.There were different responses of SOD,POD,CAT and MDA to SO₂ stress of Sc.However,under SO₂ stress,the activities of antioxidant system enzyme activities and MDA content were overall declined significantly.(4)The maximum absorption of S element of Eg,Cp,Sc and Cs were 1.17,1.32,2.04,0.95 g·kg^-1,respectively.(5)The order of the comprehensive resistance calculated based on membership function was Cp>Sc>Eg>Cs,which was consistent with the results of injury of leaves.This study suggests that the antioxidant system enzymes play a important role in resistance of SO₂ stress for the four species of young trees and the extremely high level of basic POD activity in Cp may be one of the key mechanisms of resistance of SO₂ stress.