Abstract: In this study, the mineralization and decomposition of autotrophic microbe assimilated carbon (new carbon) and native organic carbon in three upland and three paddy soils in subtropical China were measured using the ¹⁴C-labelled tracer technique. The results showed that, during the 100-d incubation, the mineralization of the ‘new carbon’ displayed three stages: a rise in the first 10 days, a slowdown from 11-d to 50-d, and a stabilization stage after 50 d. The mineralization ratio of the ‘new carbon’ ranged between 8.0% and 26.9% and the mineralization rate ranged from 0.01 to 0.22 μg ¹⁴C·g^-1·d^-1 (0.01-0.22 μg ¹⁴C·g^-1·d^-1 in paddy soils and 0.01-0.08 μg ¹⁴C·g^-1·d^-1 in upland soils). However, the mineralization ratio and rate for native SOC were 1.55%-5.74% and 1.3-25.66 μg C·g^-1·d^-1, respectively. In the soil active C pools, the ¹⁴C-dissolved organic carbon (DOC) first rose by as much as 0.3 mg·kg^-1 in the early stages of incubation (0-10 d), decreased rapidly by 0.42 mg·kg^-1 from 10-30 d, and then declined gradually. The fluctuation of the ¹⁴C-microbial biomass carbon (MBC) differed from that of the ¹⁴C-DOC. At the beginning stage of the incubation (0-10 d), the ¹⁴C-MBC decreased rapidly, and then rapidly increased from 10 to 30 d, and the rate of increase reduced and was gradually stabilized after 40 d. The ¹⁴C-DOC/DOC renewal rate in the paddy soil was significantly higher than in the upland soil while the ¹⁴C-MBC/MBC renewal rate in the upland soil was significantly greater than in the paddy soil.