Root is the principal plant organ for nutrient and water uptake, and the place for transformation, synthesis, and assimilation of plant materials. Enzyme activity and morphological characteristics of root are closely related to crop yield and quality. Previous researches have investigated management practices, such as variety, tillage, fertilization, and irrigation, which affect enzyme activity and morphological characteristics of rice root. Planting winter crop is a common practice in double-cropping paddy fields in southern China. Several cereals, grasses, and legumes have been used as winter crops to improve physical, chemical, and biological properties of paddy soil. Winter crops are also beneficial for soil erosion control and environmental amelioration. Nevertheless, the effects of planting winter crops on soil enzyme activity and morphological characteristics of rice root in double-cropping paddy fields are unclear. The objective of this study was to investigate the effects of winter crops, including potato (Solanum tuberosum L.), Chinese milk vetch (Astragalus sinicus L.), and rape seed (Brassica napus L.), on yields and enzyme activity and morphological traits of root in subsequent rice crops using a 7-year experiment located in Changsha city, Hunan province. Chinese milk vetch was seeded directly at the end of September (approximately 20d before the harvest of late rice), and harvested in the middle of April. Rape seed and potato were transplanted at the end of October and harvested at the end of April. At the harvest of Chinese milk vetch, rape seed, and potato, about 22500 kg/hm², 7500 kg/hm², and 22500 kg/hm² straw was returned to the field respectively. Crop yields of early and late rice were estimated at harvesting time from 2005 to 2011. Rice roots were sampled to estimate enzyme activity and morphological characteristics at typical growth stages of early and late rice crops in 2011. In comparison with the control (winter fallow), inclusion of winter crops increased root malondialdehyde (MDA) content in early growth stages for both early and late rice crops. No significant difference was found between all the treatments in late growth stages for both early and late rice crops. Winter crops also improved the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in the roots of subsequent rice crops, which were helpful for remitting cell membrane peroxidation. Root morphology traits of the succeeding rice crops varied with preceding winter crops. Planting potato and Chinese milk vetch promoted root growth of early and late rice crops, thus increased rice yield by 6.29% and 7.76% in 2011, respectively. On the other hand, planting rape seed inhibited root growth of late rice and decreased late rice yield by 6.31%, and double rice yield by 1.96%. Correlation analysis indicated that under potato and Chinese milk vetch treatments, the greater length, number, volume, and surface area of rice roots at grain filling stage were major factors contributed to the improved double rice yields. No significant correlations were observed between yield and enzyme activities (MDA, SOD, POD and CAT) of rice. We concluded that potato and Chinese milk vetch were beneficial winter crops for improving root growth and yield of double rice, while rape seed was not recommended as a suitable winter crop in double cropping rice production. In addition, environmental and economic effects should be considered when selecting winter crops.