This study aims to explore the association between early sex initiation and subsequent unsafe sexual behaviors and risks among Chinese female undergraduates. Of 4769 participants, 863 (18.1%) reported ever having sexual intercourse. The mean age of sexual debut was 19.3 (+/- 1.7) years. Females initiating sex earlier were more likely to have first sex with men who were not their boyfriends and less likely to take contraception, to use a condom at first encounter, to use contraception consistently in past year, and/or to use condom consistently during the course of a sexual intercourse. They were more likely to have multiple lifetime and concurrent sexual partners, to report pregnancy, and be diagnosed with sexually transmitted diseases. Comprehensive early sex education should be advocated for young people, not only teaching knowledge of physical health but also providing practical skills training for making them consciously delay start of sexual activity or protecting themselves during sexual intercourse.