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Here, we aimed to understand the effects of nitrogen (N) -fixing and non-N-fixing tree species on the stoichiometric characteristics of soil carbon (C), N, phosphorus (P), and soil readily oxidized carbon (ROC) in south China. We determined the levels of soil total organic C (TOC), total N (TN), total P (TP), and ROC in 13-year-old Acacia crassicaipa and Eucalyptus urophylla plantations in Heshan, Guangdong Province, to analyze their characteristics and correlation of N-fixing and non-N-fixing tree species after afforestation. The results showed that soil ROC and TOC contents in N-fixing tree stands were significantly higher than those in non-N-fixing tree stands (P＜0.05), and ROC/TOC values were lower in the N-fixing than the non-N-fixing tree stand soils, indicating that soil C stability was improved in the N-fixing tree stand soils compared to the non-N-fixing tree stand soils. The soil TN content and C: N value were significantly higher in the N-fixing stands than in the non-N-fixing stands (P＜0.05). Soil C: P, N: P, and C: N: P were higher in the N-fixing stands, but the differences were not statistically significant. Soil TOC and TN were positively correlated in both stands (P＜0.01). In N-fixing stands, soil TOC and TN were negatively correlated with ROC/TOC (P＜0.05), and soil water content (SWC), C: P, and N: P were significantly positively correlated with TOC (P＜0.05). In south China, where SWC is high, afforestation with N-fixing trees increased soil TN and TOC contents and soil stoichiometric ratio, which helped improve soil C stability. [ABSTRACT FROM AUTHOR]