Introduction: The World Health Organization (WHO) defines adolescent people as thosernbetween the ages of 10 to 19 years. These age groups are often characterized as being at a lifernstage of increased experimentation and exploration associated with a range of risky behaviors,rnincluding risky sexual behaviors. Moreover, adolescents are less likely than adults to have therninformation, skills and support to protect themselves against HIV/AI DS and other consequencesrnof premarital sex.rnObjective: To assess the prevalence of premarital sex and unprotected sexual intercourse practicernand associated factors among secondary school adolescent students in Sebeta Town, 2014.rnMethods and Materials: A questionnaire based cross sectional study design was used to conductrnthis study on 284 secondary school adolescent students in Sebeta Town from April to May 2014.rnThe data was processed and analyzed by using Epi Info 3.4.3 and SPSS version 16.0. Frequencyrndistribution, charts, figures and tables were used to present the results. Odd ratio and logisticrnregression were used to determine association between specified factors and to controlrncofounders respectively.rnResults: The prevalence of premarital sex among the study participants of this study was 28.3%rnand 90.1% of them were utilized condom during their sexual intercourse. The premarital sex wasrnstrongly associated with grade level and their family income. Grade ten students were 7.99 timesrnhigh risk to be practiced premarital sex than others (AOR=7.99, CI= (2.2-28.5)) and grade elevenrnstudents were 7.81 times high risk to be involved in premarital sex than others grade levelrnstudents (AOR= 7.81, CI= (2.4-25.4)). Students belong to family earned 500-1000 ETB werern2.47 times high risk to be experienced premarital sex than others students (AOR= 2.47, CI=rn(1.01-6.07))rnConclusion: The prevalence of premarital sex among the study participants was higher than thernstudies conducted in different parts of Ethiopia and almost all of the students who have hadrnhistory of sexual practices utilized condom during their sexual intercourse. Premarital sex amongrnthe study participants of this study was strongly associated with studentsâ€˜ grade level and familyrnmonthly income status.rnRecommendation: Ministry of Health, Ministry of Education and schools in collaborationrnshould provide psychosexual services for adolescent students at secondary school level.rnKey words: premarital sex, unprotected sex, adolescent students, Ethiopia.