Introduction: In recent years, overweight and/or obesity among children and adolescents have emerged as a global epidemic. Overweight and/or obesity during adolescence predispose them to the development of cardiovascular and metabolic disorders in adulthood. However, information regarding overweight and/or obesity is still scarce for primary prevention. Thus, this study aimed at assessing prevalence of overweight and/or obesity and factors associated with them. Methods: Institution based cross-sectional study was employed. The participants were 800 high school adolescents aged 15–19 years selected using multistage sampling technique. Body mass index (BMI) was used to determine the nutritional status. Univariate, bivariate and multivariate analyses were considered. Results: The overall prevalence of overweight and/or obesity was found to be 75 (9.4%). Having small family size (AOR=3.10 95% CI: 1.69-5.53), learning in private school (AOR=2.73 95% CI: 1.36-5.49), being with lower middle income family (AOR=2.40 95% CI: 1.07-5.37) and living in male headed household (AOR=2.56 95% CI: 1.25-5.24) were significantly and positively associated with overweight and/or obesity. Adolescents in 15-17 years of age (AOR=0.44 95% CI: 0.25-0.75) and those who were walking at least 30 minutes in a day (AOR= 0.40 95% CI: 0.19-0.65) were negatively associated with overweight and/or obesity. Conclusion: This study revealed that overweight and/or obesity are becoming major public health problem. Learning in private school, having small family size, being in male headed household and living in lower middle income household were positively associated with overweight and/or obesity. Early adolescents and those who walk at least 30 minutes per day have inverse relationships. This study showed that promoting active lifestyles and healthy diets should be national public health priority.