Catabolism is tightly coupled to anabolism in substrate-limited cultures. However, the dissolved organic carbon (DOC) distribution between catabolism and anabolism has been hardly studied. Based on a balanced DOC reaction, the DOC distribution between catabolism and anabolism was defined using a ratio of the DOC channeled into CO2 (S-CO2) to that DOC converted to biomass (S-g). A S-CO2/S-g-dependent growth yield model was proposed for substrate-limited cultures and was verified using the literature data obtained in the oxidative assimilation processes of different types of organic substrates. The model showed that the growth yield (Y-s) was proportional to anabolic activity, but was inversely related to catabolic activity. Results indicated that both Y-s and S-CO2/S-g varied markedly with the free energy of oxidation of the organic substrate. Further, the observed phenomena were closely associated with maintenance metabolism under substrate-limited conditions.