Background: Early initiation of sexual activity has been escalating among young people.and it leads to risky sexual behaviors. This might lead to health and health related burden among youth. In order to prevent this problem as well as to implement youth reproductive health (RH) programs effectively conducting different reasearches is necessary. Objective: To assess the age of first sexual debut and condom use among in school youth in Debre Markos town Method: A cross sectional study was employed in Debre Markos town from December, 2013 to December, 2014. The study populations were secondary school students in the town. Seven hundred students were selected from three secondary schools. Self administered structured questionnaire and in depth interview was a method used to collect data. Data entered into EPI-info software and analyzed using the SPSS statistical package. Descriptive statistics, Chi square test, bivariate and multivariate logistic regressions were used. Result: About a fifth (22.3%) of study participants started sexual intercourse at the time of the study. The median age at first sexual intercourse was 16. Socio-demographic factors such as being grade nine (AOR =5.5: 95%CI (1.2, 25.6), living with renting alone AOR=1.7:95%CI (1.2, 17.6) and getting less than 100 birr/month pocket money AOR=5.1:95%CI(1.1,26.0)were significantly associated with early sexual activity. Similarly, students who did not hear about the negative effect of early sexual activity AOR=3. 5:95%CI (1.1, 11.2) and who did not agree with the idea of their parental connection and supervision might postpone sex AOR=3.5:95% CI (1.1, 10.7) significantly associated with early sexual debut. Majority 109 (69.9%) did not use any family planning method including condom at the time of their first sexual intercourse. Those who planned their first sexual intercourse (36.5%) and who had willingness to get condom themselves (36.8%) used condom more than their counterparts. Those who got more than 200 Birr per month pocket money (AOR=5.7: 95%CI (1.1, 29.9) were used condom more at last sexual intercourse. Among student’s community norms, lack of comprehensive knowledge and misconception about condom is a reason not using condom during sex Conclusion: Age of sexul debut among high school students was low in the town. Students’ knowledge about early sexual activity influence to start sex at earlier age. Parental connection and supervision has a role to start sex at earliy age.Use of condom or other family planning method at first sexual intercourse among student was low. Students who are not willing to get condom themselves used condom lower than others. Recommendation: In order to decrease early sexual activity, equip students with comprehensive sexual health knowledge is a crucial work. This could be done by the collaboration of family, governmental and non governmental organizations. Condom use at sex might be increased by improving their willingness to get condom themselves. Awareness creation in the community and avoiding misconception could be a a strategy.