Objective To analyze the factors affecting weaning-to-service interval(WSI) of sows, estimate genetic parameters of WSI in sows, and provide theoretical references for pig breeding program.Method The research data are the reproductive records of Yorkshire and Landrace in two farms (A and B) of South China collected from 2011 to 2016. Duncan's method was used to analyze the factors affecting WSI of sows. The genetic parameters were estimated using AI-REML of DMU software combined with EM algorithm.Result Parity and weaning years had highly significant effects on WSI of sows (P<0.01). Weaning season had highly significant effect on WSI of Landrace sows in both A and B farms and Yorkshire sows in B farm (P<0.01), while it had no significant effect on WSI of Yorkshire sows in A farm (P>0.05). The number of suckling piglets had no significant effect on WSI of sows in both farms (P>0.05). The heritabilities of WSI in Yorkshire and Landrace sows in A farm were 0.02 and 0.04 respectively, and the heritabilities of WSI in both Yorkshire and Landrace sows in B farm were 0.06.Conclusion The WSI of sows in South China is a low heritability trait, which is significantly affected by parity and weaning season. In practical production, the WSI of sows after first delivery should be shortened,and the sows should be weaned in cold season.