Abstract: This research was conducted to determine the effect of increased tropospheric CO2 and O3 on responses of soil basal respiration rates (BR) and microbial population (MP) in soybeans (Glycine max) rhizosphere soil. Significant changes in BR, qCO2 and MP were observed for all treatments. The greatest increases in BR and MP and the least in qCO2, were found at early grainfill stage treatments. The deterrence in BR and MP values were stimulated by the increase in CO2 singly, or in combination with high O3 exposures compared with CF control. Reductions in BR and MP observed for NF + (30±5 nL O3 L-1) treatments during flowering and early grainfill stages, thus suggests that O3 injury can reduce the BR by decreasing the activity of microbes in soil. This study suggests that carbon dioxide could decrease the harmful effect of ozone on soybean plants.