Primary dysmenorrhea is common problem among adolescent which can have negative effects on their daily activities .Aim: to evaluate the effect of stretching exercise on primary dysmenorrhea among secondary girl students at Assiut city. Subject and Methods: Quazi experimental research design was used in this study included 666 students, while the students having dysmenorrhea 515 were selected by using multi stage random sample and the program implement on169 students from Assiut city. Through a period from September 2018 to the April 2019. Four tools were used for data collection, first tool: A structured self-administered questionnaire which consisted of two parts: first part included personal characteristics, second part: knowledge about menstruation and dysmenorrhea of adolescents girls. Tools (II):Verbal Multidimensional Scoring System, tools (III): Visual Analogue scale used to assess the severity of dysmenorrhea. Tools (IV):observational checklist was used for evaluation stretching exercise. Results: The mean age of students ±SD was 16.31±0.9 (15.0-19.0).Regarding to the prevalence of dysmenorrhea among studied students, it was found that more than three quarters(77.3%) were suffering from dysmenorrhea .Conclusion: It was found that there was a statistical significant difference regarding the degree of dysmenorrhea and stretching exercise.   Recommendation: Improve student's awareness and knowledge about effect of physical stretching exercise by incorporating this topic into curriculums.