Background: - Premarital sex is common among high school and preparatory school students. It increases the risk of HIV/AIDS, unintended pregnancy, unsafe abortion and psychosocial problems. It also exposes adolescents to the risks of other STIs and school dropout. Objective:- To assess the magnitude of premarital sexual practice and associated factors of students in secondary and preparatory school at woreta town, south Gondar zone of Northwest Ethiopia in 2019. Methods:- Institutional based cross-sectional study was conducted among secondary and preparatory school students. Stratified random sampling technique was used to select the sample students to take part in the study. All regular students (secondary and preparatory) who were attending class at the time of the survey in woreta town secondary and preparatory schools were divided into different strata. Data was collected using a structured, self-administered questionnaire adapted from previous studies. Data was, coded and entered into EPI- INFO version 7 and exported into SPSS version 23.0 and analyzed. Binary Logistic regression model and multivariable regression were fitted to identify factors associated with premarital sexual practice. Results: - over all, 31.8 % (95%CI: 28.3, 35.5) reported pre-marital sexual intercourse. Significantly associated factors were: being female (AOR=7.02, 95% CI 4.13,11.91) ,grade 11,(AOR=3,95%CI,2,6) grade 12 (AOR=4.3,95%CI,2.35,8),not attending religious education(AOR=2.39,95%CI,1.44 ,4), having pocket money (AOR = 2.10,, 95% CI 1.33, 3.26), drinking alcohol(AOR=4,95%CI,2.4,6.6) ,peer pressure(AOR=5.9,95%CI,2.78,12.73),watched pornographic film(AOR=9.83,95%CI,4.6,21.02) and adolescents who did discuss sexual issue with close friends (AOR = 1.89, 95% CI 1.12, 2.94). Conclusion: - In this study medium prevalence of premarital sexual practice has been reported. Sex, grade level, Not attending religious education, pocket money, alcohol drinkers, watching pornography film, peer pressure and discussion sexual issues with close friend were factors that affect premarital sexual practice. Keywords:-premarital sexual practice, Woreta and School adolescents