Background: Risky sexual behaviors are any behavior that increases the probability of adverse sexual and reproductive health. Adolescent and young aged 15–24 years are at particularly high risky sexual behaviors. Risky sexual behaviors predispose adolescent and young people to a variety of sexually associated problems. Objectives: The objective of the study is to assess the magnitude of risky sexual behaviors and its associated factors among night school students in Arada sub-city 2017. Methods: A cross-sectional quantitative study design method complemented with qualitative method carried out among night school students in Arada Sub-City, Addis Ababa, Ethiopia. Five hundred forty individuals were selected from a total of 3,641 by multi- stage sampling method. The data were collected by using pre-tested structured self-administered questionnaire. Data were entered into Epi-Info version 7 and analyzed using SPSS version 24 software. Result: A total of 540 night school students were enrolled in the study with response rate of 514 (95.2%) among those 317(61.7%) of the study participants were females; 342(66.5%) the study participants had sexual experience and only 78 were married. Among the sexually active students 139(40.4%) reported that they had two or more sexual partners in their lifetime, 127 (37.1%) reported sexual contact with casual person, 26(7.6%) with commercial sex workers and 222 (64.9%) had risky sexual behavior. Multivariable logistic regression analyses showed that males are 1.676 times more likely to have risky sexual behaviors than females [AOR= 1.676 (95% CI: 1.026-2.741)] and being in 15-19 age group 0.593 times less likely to have risky sexual behaviors than 20-24 years [AOR= 0.593 (95% CI: 0.363- 0.739)]. Similarly being single and divorced participants were 3.326(1.737-6.368) and 3.939(2.043-7.595) with 95% CI times higher risky behaviors respectively. Practicing sex after drinking alcohol were [AOR = 4.858 (95% CI: 2.314-10.196)] and sex after watching pornography were [AOR = 3.964 (95% CI: 1.559-10.078)] associated with risk sexual behaviors. Conclusion: Significant number of night school students had two or more sexual partners and sex with sex workers had risky sexual behavior that might predispose them to different sexual and reproductive health problems. Reducing risky sexual behavior among night school students can be achieved through multi-sectored responses in the school.