Abstract: To understand the effects of elevated atmospheric O₃ (eO₃) by 40 nL·L^-1 on carbon (C),nitrogen (N),phosphorus (P) and potassium (K) concentrations in soybean seeds,we analyzed corresponding stoichiometric ratios in open top chamber (OTC) simulation systems using 3 soybean cultivars Dongsheng 1,Suinong 4 and Suinong 8.Results showed that across the 3 soybean cultivars,eO₃ decreased soybean seed C and P concentrations on average by 1.51% and 10.7%,respectively,but increased seed N and K concentrations on average by 37.8% and 11.0%,respectively.Although significant variations of C,N,P and K concentrations in soybean seeds existed among different soybean cultivars,the interaction of O₃×cultivar on seed C,N,P and K concentrations was not significant.eO₃ increased soybean seed C/N and C/K,decreased C/P and N/P but increased P/K simultaneously.This indicate that the use efficiency of N and K in soybean reduced by eO₃,while the utilization of N under eO₃ may be limited by P but not K.