The relationship between microbial biomass N and total N mineralization dynamics in paddy soils of subtropical China was investigated by lab incubation experiment. Results showed that the amount and rate of soil microbial biomass N mineralization decreased with the incubation time but increased with the promotion of soil fertility. During 12 weeks incubation, more than half of microbial biomass N was mineralized, in which half was occurred in the first 4 weeks. The cumulative N mineralization in paddy soils ranged from 73.0 to 127.8 mg/kg, and the rates ranged from 6.09 to 10.7 mg/(kg·wk). Two component equation and dynamic equation could simulate microbial biomass N and total N mineralization, respectively. Both the microbial biomass N and total N mineralization processes could be divided into two periods: rapid mineralization period in the first 8 weeks and thereafter slow mineralization period. The comparison between parameters in two equations showed that the proportion of microbial biomass N mineralization in soil total N mineralization varied from 10.8% to 49.5%. Microbial biomass N has a large mineralization potential and continuously-rapid turnover capacity. It plays an important role in maintaining soil nitrogen supply.