Based on the monitoring of soil fertility, this paper studied the characteristics of microbial biomass C (MBC) and N (MBN) in paddy soils derived from different parent materials in Hunan Province. The results showed different fertilization systems had different effects on soil MBC and MBN. After 18 years fertilization, the MBC and MBN in different paddy soils had similar variation trend, with the sequence of paddy soil derived from lake sediment > from river alluvium and quaternary red earth > from limestone > from shale. Soil MBC content ranged from 259.5 to 864.4 mg x kg(-1), while MBN ranged from 8.7 to 70.7 mg x kg(-1). Fertilization could increase soil MBC and MBN markedly. Organic fertilizer was the main element for the promotion of soil MBC and MBN, and combined application of organic and inorganic fertilizers could obtain the greatest effect. The increment of soil MBC and MBN after applying inorganic fertilizer and its combination with organic fertilizer was 407.6 and 59.2 mg x kg(-1), in maximum, and the maximum increasing rate was 102.8% and 514.8%, respectively, compared with no fertilization.