Abstract: The impacts of O₃ and CO₂ concentration doubling on the soybean leaf development and biomass are studied by using OTC-1 open top chambers.The results show that O₃ and CO₂ concentration doubling can lead to the yellow leaf ratio increase and the green leaf ratio decrease.CO₂ concentration doubling causes positive effects on the soybean leaf area，leaf weight，weight of green leaf and yellow leaf，as well as biomass，while O₃ concentration doubling causes negative effects on those.The mixed ozone and carbon dioxide may alleviate the negative effect of ozone on soybean biomass.The negative effect of O₃ on soybean leaf is more obvious than CO₂ in O₃ and CO₂ combination lasting concentration doubling. Before the bulge kernel stage，the alleviating effect of CO₂ on soybean leaf is apparent in the treatment of O₃ and CO₂ in combination gradually to concentration doubling；while after the bulge kernel stage，the effect of CO₂ and O₃ on soybean leaf is similar，the increasing of soybean biomass follows the curve of natural growth.