Rubber-based (Hevea brasiliensis) agroforestry systems are the best way to resolve the environmental problems caused by rubber monoculture. Rubber Flemingia macrophylla (nitrogen-fixing plants) systems have become popular in Xishuangbanna, Southwest China. Soil water content and exchangeable cations (Ca2+, Mg2+, K+, and Na+) are important for sustainably managing forest ecosystems. In this study, we investigated the responses of soil water content and exchangeable cations in rubber and rubber Flemingia macrophylla systems. Soil water content increased in the 0-90 cm soil layer as the rubber plantations aged, and the mature rubber plantations had similar soil water storage to rainforests. The rubber plantations use soil water in the 30-90 cm soil layer to avoid drought stress during the long, dry season. The introduction of Flemingia macrophylla to the young rubber plantations significantly increased soil water depletion in the 30-90 cm soil layer. The introduction of Flemingia macrophylla to the mature rubber plantations had no significant effects on soil water in the 0-90 cm soil layer. The introduction of Flemingia macrophylla to the differently aged rubber plantations mitigated soil acidification by decreasing nitrogen inputs. The total exchangeable cations in the 0-90 cm soil layer sharply decreased as the rubber plantations aged due to the acceleration of soil acidification. When soil pH was below 5.5, 7.85 cmol kg(-1) of soil exchangeable cations were released when the pH decreased by one unit. However, the introduction of Flemingia macrophylla to the differently aged rubber plantations effectively reduced the release of soil exchangeable cations by mitigating soil acidification. In conclusion, rubber Flemingia macrophylla systems can mitigate soil acidification and reduce the release of soil exchangeable cations relative to rubber monoculture.