Masson pine (Pinus massonianas Lamb.) seedlings were exposed to SO_2in 3 open top chambers (OTC) for 60 days and nights, in which the concentrations of SO_2 were 0.0 mg/m~3 (CK), 0.2 mg/m 3 and 0.4 mg/m~3 , respectively. In the treatment of SO_2 0.2mg/m~3, no abnormity of stomata cells, needle colour,and roots was been observed. There were no significant difference in chlorophyll content, photosynthetic rate, and transpiration rate compared with the control. However, compared with control, the carotenoid ...