Abstract: Objective： To investigate the communication about the sex-related issues between parents and their unmarried child (children), and to analyze the factors influencing communication. Methods：The stratified，multi-stage and cluster sampling，as well as structured questionnaire survey were used for data collection. Results：A total of 2 871 mothers and fathers who have at least one unmarried child aged 15 to 24 years were investigated. Topics communicated between parents and unmarried child were mostly on child's school study and career，and rare on sex-related issues. Problems encountered in parental-unmarried child communication about sex-related issues were mainly three as follows. ①Parents and their children feel shy（about 50%）. ②Parents didn’t know how to talk about such issues with their unmarried children （about 26%）.③Parents thought themselves being lack of knowledge related to sex （about 13%）. Parental socio-demographic characteristics，such as gender，age，education level， occupation and parental-child relationship, had different influence on parental-child communication about the sex-related issues. Conclusions：At present, the family-based sex education should be a public concern，particularly to develop strategies to increase parents' awareness and capacities in communicating with their unmarried children.

Key words: Parent-child relations, Sex education, Communication disorders, Questionnaires