Abstract: 【Objective】This study explored the characteristics of nitrogen(N)mineralization and nitrogen supply capacity in a Karst primary forest and a secondary forest.【Method】A Karst primary forest and a secondary forest were chosen as study sites. Temporal variations in soil N mineralization and nitrification were determined in situ by continuous incubation by using the resin-core method.【Result】① With an increase in incubation time, the content of soil inorganic N in both the primary forest and the secondary forest showed pronounced variation. The NH⁺₄-N contents firstly increased, then decreased and finally increased, while NO^-₃-N contents generally increased. The NH⁺₄-N was the main form of inorganic N, and accounted for 84.57%-94.31% of the soil inorganic nitrogen. ② The mineralization rate had a ‘V' shape, and its ranges in primary forest and secondary forest were -0.43-0.97 mg/(kg·d)and -0.91-1.43 mg/(kg·d), respectively. Nitrification rates tended to increase, and were 0.21-0.49 mg/(kg·d), 0.03-0.31 mg/(kg·d), respectively. ③ The inorganic N content and rates of net nitrogen mineralization, nitrification, and ammonification in the primary forest were higher than those in the secondary forest. ④ The annual net amount of N mineralization was 170.82 kg/(hm²·a)in the Karst primary forest, 2.48 times that in the secondary forest. Nitrified N in the primary forest and the secondary forest were 95% and 100%, respectively, of mineralized N.【Conclusion】The soil in the Karst forest had a relatively high capacity for supplying N, and soil nitrification played a dominant role in the process of soil N mineralization, indicating that the available N was volatile or easy to leach.