Background: Risky sexual behavior is any behavior that increases the probability of negative consequences associated with sexual contact. Family environment, peer influence, community factors and school attachment seem an important factor affecting sexual risk behavior and decision of in-school youths. Objective: To assess sexual risk behaviors and associated factors among students living with parents in Jimma zone preparatory schools. Methods: A cross sectional study designs both qualitative and quantitative approaches was conducted in 5 randomly selected preparatory schools. A total of 273 students were randomly selected. Multiple logistic regressions were performed to identify the independent predictor of risk sexual behavior. Result: One hundred fiten (42.1%) students had sexual risk bahivor. Thirty six (30.8%) student's reports they had two or more sexual partners in their lifetime. Out of 117 students, 13 (11.2%) students used condom always. One hundred one (37%) students were consumed alcohol. Higher likelihood of risky sexual behavior significantly associated with higher levels of alcohol consumption and low frequency of religious visit. Conclusion: Alcohol consumption and religious visit were the major predictors of risky sexual behaviors. Therefore, Behavior change communication should consider family environment and other factors which predict risk sexual behaviors.