With the increasing demands for wood resources under the social development, large areas of natural forests in China have been transformed into secondary forests or plantations. Different forest types can have profound effects on ecosystem structure and function. We examined the responses of the abundance of nifH genes in soils and aggregates to forest types, including Cunninghamia lanceolata plantation and Pinus massoniana plantation formed by reforestation after clearcutting of natural Castanopsis carlesii forest, as well as secondary C. carlesii forest formed after selective logging. Results showed that soil available phosphorus (AP) and soil moisture contents in both plantations were higher than those in the secondary forest. P. massoniana plantation had significantly higher AP content than the secondary forest and C. lanceolata plantation. The abundance of nifH genes (4.26×10⁹ copies·g^-1) in P massoniana plantation was significantly higher than that in secondary forest (2.16×10⁹ copies·g^-1) and C. lanceolata plantation (3.07×10⁹ copies·g^-1). The abundance of nifH genes was significantly and positively correlated with AP and moisture contents in bulk soils. Moreover, aggregate sizes had a significant effect on the abundance of the nifH genes, with the lowest abundance in silt-clay particles and the highest in small macroaggregates in all forest types. The abundance of nifH genes in different sizes of aggregates from the P. massoniana plantation was generally higher than that from the secondary forest and C. lanceolata plantation. Overall, both forest types and soil aggregate sizes significantly influenced the abundance of nifH genes in subtropical forests, with AP and moisture contents as the critical driving factors.