The study of adolescent sexual behavior in Viet Nam is of great interest to social researchers as sexual behavior, particularly among adolescents, is changing along with social and economic development. Using data collected from 800 single male students by face to face interviews from a survey of reproductive behavior of unmarried urban students aged 17-24 in 8 universities in Ha Noi and Ho Chi Minh city, Viet Nam. This study attempts to model the factors that influence premarital sexual behavior among male students. The study also provides recommendations to policy makers and educators to develop appropriate curricula and materials to help students increase their knowledge, and to help them to engage in more responsible and safe sex behavior. Overall, the results indicate that the sample comes from largely stable families and have parents with relatively high education. Many of the respondents are living apart from their families. The findings show that adolescents seem to be relatively liberal and open-minded in their attitudes towards sex and sexual behavior. However, most respondents do not accept casual sexual relationships. Knowledge about contraception is limited, but most respondents had good knowledge about STDs/HIV/AIDS. Only 14.8 per cent of respondents reported having had sexual intercourse. The mean age of first sexual experience is relatively high (19.5 years old). Factors influencing the practice of premarital sexual activity are background characteristics, attitudes toward sex and knowledge about contraception, and STDs/HIV/AIDS. The age of respondents has a strong effect on the probability of having engaged in premarital sex. Place of residence, marital status of respondents parents and current living situation affect attitudes toward sex and premarital sex in bivariate analysis, but these effects were reduced, and even eliminated, when other variables are entered in the model. Mothers education had no significant effect on attitudes toward sex and practice of sexual activity before marriage in both bivariate and multivariate analysis. Knowledge of contraception and STDs/HIV/AIDS had no significant effect on either attitudes or premarital sexual behavior. Attitudes toward premarital sex and casual sex have strong significant relationships with sexual experience before marriage. Although perceived attitudes of peers toward premarital sex had a strong effect itself, and combined with background variables, it had no statistically significant effect when all variables were entered into the model and appears to be operate through the effect of respondents own attitudes.