Root exudation of organic acids is an important strategy for plant acquisition of phosphorus (P) from P-deficient soils. In tropical rain forests, soil weathering generally results in a decrease of P availability, which may influence dynamics of organic acids in the rhizosphere. We quantified the rates of root exudation and mineralization in the podzolic (older) and younger soils of Mt. Kinabalu, Borneo by measuring the concentrations of oxalate, citrate, and malate in root exudates and soil solution and the mineralization kinetics of ¹⁴C-radiolabelled organic acids. The root exudation rates of organic acids were greater in the P-deficient podzolic soil than in the P-rich younger soil. In the podzolic soil, the rhizosphere contained markedly higher concentrations of organic acids than did the bulk soil, whereas in the younger soil, the levels of organic acids were lower. The mineralization kinetics showed that oxalate and citrate could be rapidly mineralized, having short mean residence times (1.0 to 2.3 h). Despite rapid biodegradation, the higher level of organic acids in the rhizosphere can be maintained by the greater input by root exudation and the lower anion sorption capacity in the podzolic soil. The P-deficiency caused by podzolization appears to result in the increased exudation of organic acids and their rapid biodegradation in the rhizosphere.