This study was conducted to determine the relationship of stomatal responses, photosynthesis, and intercellular $CO_2$ concentration( $C_{i}$) of Betula Species to ozone exposure. Five Betula Species(B. costata, B. davurica, B. schmidtii, B. platyphylla var, iaponica and B, ermani) were grown in the greenhouse. One-year-old potted seedlings of the five Betula Species were exposed to ozone(100 pub) for 8 hours da $y^{-1}$ for 5 weeks in a fumigation chamber. Net photosynthesis was significantly different among species and treatments from early in the period of the fumigation. Stomatal conductance and transpiration rate differences among species and treatments became significant after three weeks of fumigation. $C_{i}$ was significantly different only among treatments; $C_{i}$ of four species, except for B. davurica, was higher than that of control plants. Carboxylation efficiency and photo-respiration rate were significantly different among species or treatments; carboxylation efficiency and photo-respiration rate of the five Betula Species were decreased by ozone treatment. It was concluded that stomatal closure of Betula Species may be the result of the reduction of photosynthesis and rubisco activity and the resulting increase of $C_{i}$. The higher $C_{i}$ likely resulted from reduced photosynthesis because of physiological processes.ocesses.