Soil organic matter (SOM) is the largest carbon pool in terrestrial ecosystems, with its temperature sensitivity playing an important role in the carbon (C) cycle and C sink at the ecosystem level. To elucidate how changes in vegetation types (primary forest versus secondary forest) influence SOM decomposition, we assessed a deciduous broad-leaved primary forest and secondary forest in the Changbai Mountains in the study, respectively; Soil samples from each forest type were incubated under different moisture (30%, 60% and 90% saturated soil moisture (SSM)) and temperatures (5, 10, 15, 20, 25 and 30 ℃) condition. Then, SOM decomposition rates were measured at 9 times over 56 d incubation period. It was found that vegetation type, incubation temperature, and moisture had significant impacts on soil carbon mineralization rates, with a significant interaction among these parameters (P < 0.001). Higher accumulation of soil C mineralization occurred in the secondary forest compared to the primary forest, e.g., 346.41 μgC/g versus 241.01 μgC/g at 90% SSM and 30 ℃ temperature, respectively. The two-factor models, including temperature and moisture, provide a good fit to soil C mineralization, with both temperature and moisture explaining 82.7% to 95.9% variation in soil C mineralization. Moreover, the temperature sensitivity (Q₁₀) of soil C mineralization was significantly higher in the secondary forest than in the primary forest; however, moisture has a complex effect on Q₁₀. For example, the highest Q₁₀ was obtained for 60% SSM in the secondary forest versus 90% SSM in the primary forest. Our findings indicate that transformation from primary forest to secondary forest would accelerate the decomposition rates of SOM, resulting in a larger loss of SOM. Moreover, secondary forests with higher Q₁₀ should are expected to be more sensitive to warmer scenarios in view of SOM decomposition. In conclusion, the complex impact of changing vegetation types change and soil moisture on the soil C cycle in forests requires focused research in future studies.