This study aims at describing premarital sex behavior as well as to analyze peers impact on premarital sex behavior of teenagers. The study was conducted in Bali, Indonesia. This is an analytic observational research that applied cross-sectional approach. The subject was 566 teenagers who were studying at Senior High Schools in Buleleng, Bali. Data was collected using a questionnaire. We examined the validity and reliability of the data before analyzed it. We also collected data through interviews. After being analyzed by logistic regression analysis, the data shows that 47% of teenagers have never watched porn, 35.9% of teenagers have never conducted kissing activity (with their partner), 24.7% of teenagers have never conducted sexuality rub toward their sexual organs, 22.8% of teenagers have ever masturbated, and 13.1% of teenagers have never experienced sexual intercourse. Teenagers who have got the correct information from peers are possible to have better premarital sex behaviors, 2 times greater than those who have not got correct information (OR = 2; p = 0.003). It is also found that teenagers who have got a good emotional relationship with peers are more possible to have better premarital sex behavior life, 3 times greater, than teenagers who have got a less emotional relationship with peers (OR = 3; p = 0.000). It is concluded that, statistically, there is significant influence between peers and premarital sex behaviors of teenagers in Indonesia.