Background: Adolescence is a transition from childhood to adulthood. At this time there are physical and psychological changes. These changes cause sex drive, high curiosity, and promiscuity in adolescence opens up big chances of premarital sex behavior. Information and teenagers’ knowledge that less precise related to premarital sex can lead to the occurrence of sexually transmitted diseases, unwanted pregnancies, children born out of wedlock and abortion. One way to prevent premarital sex behavior is to increase knowledge by providing health education. Health education can use media and innovative methods to attract the intended target so that the target can absorb the material better. Innovation of health education one of them by using lecture with audiovisual. Research Objectives: This study aims to determine the effect of audiovisual lectures on the prevention of premarital sex ofadolescent in SMK YPKK 1 Sleman. Methods: The research design used quasi experimental pre and post design with cross sectional approach. Sampling technique using random sampling and the number of respondents in this study as many as 170 students. This research uses questionnaires made by the researcher and have been tested the validity of the correlation coefficient of biseral on 30 respondents with r table number 0.361 and reliability using KR-20 with result 0.891. This research was conducted in SMK YPKK 1 Sleman. Results: Respondents aged 15-17 years and majority of respondents aged 17 years. This study uses Sign Wilcoxon Test to determine the effect of audiovisual lectures on the prevention of premarital sex of adolescent in SMK YPKK 1 Sleman. The result obtained p = 0.00, so p <0.05 can be concluded that there is influence of audiovisual lecture toward prevention of premarital sex of adolescent in SMK YPKK 1 Sleman. Conclusion: There is the influence of audiovisual lectures on the prevention of premarital sex of adolescent in SMK YPKK 1 Sleman.