Abstract: It is vital to study the effects of elevated atmospheric CO₂ concentration on the soil orga-nic carbon (SOC) stability in different soil layers for better understanding the mechanism of SOC transformation under the elevated atmospheric CO₂ concentration. The paddy soil in a long-term FACE (Free Air Carbon-dioxide Enrichment) experiment was selected as the research object. Through the SOC physical fractionation and soil mineralization incubation, the effects of elevated atmospheric CO₂ concentration on the soil organic carbon (SOC) content, particle organic matter (POM) content, SOC mineralization intensity, and enzyme activities were measured. Then, the effects of elevated atmospheric CO₂ concentration on the SOC stability in different layers were exa-mined. The results showed that the elevated atmospheric CO₂ concentration had no significant effect on SOC content, but significantly increased the POM-C content by 93.7% and the invertase and polyphenol oxidase activities by 61.1% and 83.7% in the topsoil layer, respectively. These results indicated that SOC stability of topsoil was reduced under the elevated atmospheric CO₂ concentration. However, the elevated atmospheric CO₂ concentration had no significant effect on the SOC stability of deep soil layer. Our results would help assess the capacity of soil sequestrated and accumulated organic carbon and provide basis for scientific management of farmland under greenhouse effect in the future.