Abstract:One-year-old seedlings ofteak （Tectona grand/s L. f., Verbenaceae） from tissue culture were potted for simulated acid rain experiments in Guangzhou. Acid solution was prepared with H2SO4 and HNO3 adjusting to pH2.5, pH4.5 and pH6.5 for control. Seedlings were applied with acid solution once with 3 days after potting for 4 weeks from 10 June to 20 October, 2000, to study the effects of stimulated acid rain on the growth, photosynthesis and water use efficiency in teak. The results showed that the morphological parameters of the investigated seedlings were influenced significantly by acid application although no statistical difference in physiological parameters were found among treatments. The basal diameter （D） and plant height（H） of teak, particularly their combination （D2H） declined under pH4.5 and pH2.5. There were no difference in net photosynthetic rate （Pn）, transpiration rate （E） and stomatal conductance （gs） between different treatments. For all treatments, Pn was positively correlated with gs, especially under pH4.5, but the relation of E with gs was relatively low. Diurnal changes in water use efficiency （WUE） of the plants treated with pH4.5 and pH2.5 solutions were quite similar with the exception of those treated with pH6.5. The average ratio of intracellular CO2 concentration and ambient CO2 concentration （Ci/Ca） was lowest in control （pH6.5）, compared with other two acid treatments, implying that teak in the control was most effective in CO2 utilization.