Background: sexually transmitted infections (STIs) are a major global cause of acute illness,rninfertility, long-term disability and death with serious medical and psychological consequencesrnof millions of men, women and infants. In America surveillance data showed that both youngrnmen and young women are heavily affected by STI but young women face the most seriousrnlong-term health consequences.rnDue to their high prevalence, particularly in developingrnsettings, STIs result in substantial productivity losses for individuals and communities,rnparticularly where the majority of the population is less than 40 years of age. The problem ofrnreporting STIs in Ethiopia is generally thought to be similar with other developing countries.rnObjectives: the objective of this study is to assess knowledge, attitude and preventivernpractices towards STIs among Arsi Negelle town preparatory school students.rnMethodology: institutional based cross sectional quantitave study design was employed. ArnProportionaite Stratified random sampling technique was used and finally a total of 303rnrespondents were selected by using systematic random sampling method taking every 4thrnindividual for both strata. Self-administered structured questionnaire which was primarilyrnprepared in English language then translated to Amharic and afan Oromo and retranslated backrnto English by translator in order to look for consistency of the questions after completelyrncorrecting a pretest was done on 5% of the sample at other preparatory school students twornweeks prior to te actual data collection time and questionnaire was checked for completenessrnon daily basis.rnResult: a total of 303 kilture preparatory school students participated in the study nearly thernentire respondents had heard about STIs primarly from radio or TV. Only half (50.8%) ofrnrespondents had good knowdege about STIs and 54.5% of respondents were identified to havernpositive attitude towards STIs. From total participant 38.6% of them reported as they hadrnhistory of sexual intercourse.rnConclusion and recommendation: most of respondents in this study had heard about STIs inrnone or another way however only slightly near half of respondents have good knowledgernregarding the different types of STIs, causes, modes of transmission and method of prevention.rnThis study had call for continued and strengthened health education to bring change inrnrespondents bearing specifically focusing on how to overcome gender differences with respectrnto knowledge, attitude and preventive practices towards STIs.