Winter crop-rice-rice is an important cropping system in rice production region of Hunan Province. The selection of an appropriate winter crop that is beneficial to rice crop and paddy soil is critical to sustainable crop production. The objective of this study was to investigate the effects of selected winter crops on soil microbial biomass carbon, microbial nitrogen and Cmic-to-Corg in a reddish paddy soil, using an experiment initiated in 2004. The winter crops included potato, ryegrass, Chinese milk vetch, and rape seed, and fallow was used as control. The results indicated that under winter crops soil microbial biomass C and microbial N were relatively higher than under fallow. Ryegrass significantly increased soil microbial biomass C and Cmic-to- Corg, Chinese milk vetch significantly increased soil microbial biomass N, and the trends of soil microbial biomass C and N during rice growth seasons were similar among different crops. Soil microbial biomass C and microbial N under Chinese milk vetch and potato reached the maximum in mid-August.