Sulphur dioxide (SO₂) is one of the main atmospheric pollutants.It can seriously affected plants photosynthesis which is the key physiological processes of plants.Using fumigation treatment in sealed environmental control chambers,we studied the effect of different levels (concentration in natural condition,0.5 mg·L^-1,1.5 mg·L^-1 and 3.0 mg·L^-1 ) of SO₂ on content of chlorophyll,the photoresponse curve,photosynthetic parameters,diurnal variation of photosynthesis and sulfur concentration of potted saplings of Eucalyptus grandis and Cinnamomum pedunculatum.The results showed that:(1)SO₂ stress significantly decreased the content of chlorophyll a and chlorophyll b in E.grandis,while remarkably increased in C.pedunculatum.SO₂ stress made chlorophyll a/ b ratio of E.grandis was significantly lowered,for C.pedunculatum no significant effect on the ratio.(2)SO₂ stress significantly inhibited the net photosynthetic rate (P_n) of the two species.Stomatal conductance (G_s),intercellular CO₂ concentration (C_i) and transpiration rate (T_r) of E.grandis rose remarkably under SO₂ stress,and G_s and T_r of C.pedunculatum was significantly inhibited by SO₂,C_i firstly increased and then decreased.(3)Apparent quantum efficiency (AQY),dark respiration rate (R_d),light compensation point (LCP) and light saturation point (LSP) of E.grandis as well as R_d and LCP of C.pedunculatum first increased and then decreased with increasing concentration of SO₂,however,AQY and LSP of C.pedunculatum decreased.(4)In a day,SO₂ stress significantly increased P_n,G_s and T_r of E.grandis,and have no significant effect on P_n of C.pedunculatum,but lower concentrations of SO₂ stress significantly promoted G_s and T_r of C.pedunculatum.It was significantly restrained under high concentrations of SO₂ stress.C_i of both species were significantly inhibited under SO₂ stress.Sulfur content of both species showed an increasing trend under SO₂ stress.Overall,E.grandis may have a certain ability to adapt to lower concentration of SO₂ stress,but its resistance to high concentration of SO₂ stress is not as good as C.pedunculatum,which may be related to their different leaf morphology and physiological characteristics.