Influences of biochar amendments on soil organic carbon (SOC) mineralization and microbial biomass carbon and nitrogen contents were investigated in red paddy soil collected from Jiangxi Province through two incubation tests. The results showed that the mineralization rate of SOC reached maximum at the 2nd day of incubation and decreased rapidly until the 7th day, then tended to stable afterwards. Throughout the 56 days of incubation, biochar amendments of 0.5% and 1.0% reduced cumulative mineralization of SOC by 10.0% and 10.8% respectively. In addition, applying biochar significantly increased the contents of soil microbial biomass. Compared with the treatments without biochar (CK), microbial biomass carbon and nitrogen contents in soil treated with 0.5% of biochar increased by 111.5% - 250.6% and 11.6% - 97.6%, microbial biomass carbon and nitrogen contents in soil treated with 1.0% of biochar increased by 58.9% - 243.6% and 55.9% - 110.4%, respectively. In the same treatments, microbial biomass contents in drought condition (40% water-holding capacity) were higher than those in wet condition (70% water-holding capacity).The results also indicated that biochar amendments of 0.5% and 1.0% decreased metabolic quotients by 2.4% and 26.8%, microbial quotients by 43.7% and 31.7%, respectively.