Background: Adolescents in Ethiopia are exposed to various risks, such as human rnimmunodeficiency virus (HIV), other sexually transmitted infections (STIs), unwanted rnpregnancy and unsafe abortion due to unprotected sex while they have high knowledge of rncontraceptive use. rnObjective: To asses the factors affecting modern contraceptives utilization among preparatory rnschool adolescents rnMethods: A cross sectional school based study was conducted on April to May 2010 in Addis rnAbaba Administration using multistage stage sampling technique .A total of 830 students in five rngovernment and three non government schools were included in the study. A pre tested rnstructured questionnaire complemented with focus group discussion were used for data rncollection. The data entered cleaned and analyzed using SPSS version 15 software. Frequencies, rncross- tabulations and logistic regression were used rnResult Overall from 830preparatory school adolescents 159(19.2) % were sexually active .Of rnwhich 69(43.4 %) had used modern contraceptive methods. Most of the respondents used rncondom 52 (75.4%). Significantly higher proportion of male adolescents 55(79.7%) than rnfemales 14(20.3%) used contraceptives. In the binary logistic regression sex, living with friends, rnliving alone, having pocket money, discuss sexual related issue with friends, condom, shops and rnaffordable service were found to be significant predictors of contraceptive use. rnConclusion The prevalence of contraceptive use was low this showed that sexually active rnadolescents are highly exposed to the consequences of unprotected sex rnAdolescents who discus sexual related issues with their close friends were more likely to use rncontraceptive than who donâ€Ÿt rnAdolescents who had pocket money were more likely to use contraceptives than who had no rnReligious prohibition, ashamed to buy, emotional and unplanned sexual practice, fear of being rnseen by some one who knows them and trust their partner were the most frequently reported rnreasons for not to use contraceptives by school adolescents rnThe most preferred method for future use was condom and the most preferred source for future rnuse was shop rnRecommendation Establish Parents- teachers - students relationship to have free discussion rntime in order to decrease their fear and ashamed about sexuality to bring behavioral change rnSince the most affecting factor to use contraceptive by sexually active school adolescents were rnashamed to buy and emotional unplanned sexual practice, other strategies like getting the rnservice every where when they need by using modern technology should be considered rnMost of the adolescents preferred to use condom with affordable service from the shop, rnconsidering this training to the shopkeepers about the storage and supplying of condom is rnmandatory since condom can be easily affected by heat