【Objective】 Understanding of how soil organic carbon (SOC) mineralization in response to management practice and environment change is crucial for mitigating greenhouse gases emission and minimizing the impacts of forest ecosystems on climate. However, there is little information available about relationship of SOC mineralization with quantity of extraneous carbon. In this experiment, effects of addition of Chinese fir litter and its biochar (BC), on native SOC mineralization were investigated to provide certain scientific basis for building up soil fertility in Chinese fir plantations and utilizing biomass resources efficiently in subtropical China. 【Method】 In this study, soil samples (0-20 cm topsoil layer) were collected from the Cunninghamia lanceolata plantation at the Wanmulin Nature Reserve of Fujian Province. ¹³C-labeled litter (Chinese fir) and its biochar (pyrolysed at 350°C) were used as two different types of extraneous carbon (an easily decomposable carbon and a relatively stable carbon) in the indoor incubation experiment. The experiment consisted of 11 treatments, i.e. S (soil without any addition), SL₁ (soil added with 10 g·kg^-1 litter), SL₂ (soil added with 20 g·kg^-1 litter), SL₃ (soil added with 30 g·kg^-1 litter), SL₄ (soil added with 40 g·kg^-1 litter), SL₅ (soil added with 50 g·kg^-1 litter), SB₁ (soil added with 10 g·kg^-1 BC), SB₂ (soil added with 20 g·kg^-1 BC), SB₃ (soil added with 30 g·kg^-1 BC), SB₄ (soil added with 40 g·kg^-1 BC) and SB₅ (soil added with 50 g·kg^-1 BC). The carbon derived from different sources was distinguished with the ¹³C isotope technique. The soil samples were incubated at 25°C with water holding capacity kept at 60% for 28 days. 【Result】Results show that the addition of either litter or BC significantly increased the cumulative amount of CO₂, and the effect of the litter treatments was more obvious than that of their corresponding BC treatments. Cumulative CO₂ derived from added litter or BC and native SOC increased with increasing quantity of the extraneous carbon. After 28 days of incubation, 5.71%-13.68% of the litter carbon (LR-C) was decomposed, whereas only 0.34%-0.50% of the biochar carbon (BC-C) was, and 6.42-13.58 times and 2.06-3.94 times as much of the native SOC in the litter and BC treatments, respectively, as that in Treatment S was decomposed. Regression analysis shows that there was a significant linear relationship between native SOC decomposition rate and quantity of the extraneous carbon added (P<0.01). LR-C decomposition rate was positively related to addition rate of the extraneous carbon, while BC-C decomposition rate displayed a significant parabolic relationship (P<0.05) and peaked when the addition rate was 10 g·kg^-1 (Treatment SB1). 【Conclusion】 Addition of litter and BC accelerated mineralization of native SOC and the effect increased with addition rates. Compared with decomposition of litter, that of BC was less affected by microbial activity due to its lower bioavailability and higher stability in the tested soil during the short incubation period. Therefore, it may be a management practice more conducive to enhancing soil carbon sequestration of the plantations in this region, to return biochar into the soil.