The prevalence of sexually transmitted infections in China has increased dramatically over the last 20 years, and heterosexual transmission is rapidly becoming the primary route of HIV transmission. Despite this growing epidemic, little is known about the correlates of sexual behavior in young Chinese women. The objective of this study was to assess family and peer factors related to sexual behavior in Chinese female college students. Anonymously completed questionnaires were received from 4,769 unmarried female college students, recruited using randomized cluster sampling by type of university and students' major and grade. Items captured socio-demographic, family, and peer factors. To examine factors associated with sexual behavior, multiple logistic regression was used, yielding odds ratios and 95% confidence intervals. Over 18% of female students participating reported ever having sexual intercourse, of whom 31.52% had their first sexual intercourse at the age of 18 or younger with more than 50% at an age less than 20 years. Several socio-demographic, family, and peer factors were associated with ever having intercourse. Those more likely to engage in premarital sex were older; majored in art; were from one-child, richer and/or divorced families; had a mother with university or above education; had parents with a strict disciplinary style; had middle-school close friends falling in love; and had current close friends living with boyfriends. Interventions to protect young women from sexually transmitted diseases need to target early sex education and address peer and parents influences.