Using survey data of rural migrant workers in Shenzhen in 2005,this paper analyzes effects of social networks on rural migrant workers’ attitudes towards pre-marital pregnancy and extra-marital sexual behaviors.The results show that social networks is the key approach to change their marriage and sex attitudes,and number and attitudes of network members have significant effects on their attitudes towards pre-marital pregnancy and extra-marital sexual behaviors.The better the rural migrants integrate to the urban society,the closer their attitudes to those of permanent urban residents.Compared with male rural migrants,female rural migrants are less likely to accept pre-marital pregnancy and extra-marital sexual behaviors.Modernization of their marriage and sex attitudes helps their social integration into the urban society in terms of culture and value but might stimulate the occurrence of pre-marital pregnancy and extra-marital sexual behaviors.