Background: Acne vulgaris is a common disease that affects the majority of the adolescent students and a large number of young adults. Aim of study was to evaluate the effect of nutritional therapy on acne vulgaris among adolescent students. Research design: Quasi experimental research design (pre and post-test) was utilized to conduct this study. Setting: The study was carried out in all Faculties of Benha University including 15 Faculty. Sample: Convenient sample of the University students (first year) in the previous mentioned facilities, the total sample included 280 students. Tools of data collection: A structured interviewing questionnaire, which covers the following parts: 1) demographic data and medical history of the adolescent students. 2) Knowledge about acne vulgaris. 3) Reported practices about daily care of acne vulgaris andnutritional therapy practices regarding acne vulgaris. Results: 55.7% of them were female, and 66.4% of them lived in rural. 40.0% of the adolescent students affected with acne vulgaris for less than one year, 39.3% of them had oily skin, 55.7% of them had apparent pimples and 46.4 % of them had acne vulgaris in full face. 38.6 % of the adolescent students had good knowledge in pre-nutritional therapy construction and then this percentage increased to 81.8% post-nutritional therapy construction, and 67.5% of the adolescent students had unsatisfactory practices pre-nutritional therapy construction which decreased to 28.6 % post nutritional therapy construction. Conclusion: The nutritional therapy construction succeeded to improve the students' knowledge and practices daily care.  There was positive correlation between total knowledge scores of the adolescent students, total reported practices scores and nutritional therapy scores of them pre and post nutritional therapy construction. Recommendations: Develop and implement health education program for adolescent students to increase their knowledge about acne vulgaris and their practices to manage acne vulgaris, educational program to determine the effect of diet on development and severity on acne vulgaris. Further researches are needed to implement nutritional therapy on adolescent students to eat a healthy food to prevent acne vulgaris.