Background: Dysmenorrhea is the most common gynecological symptoms among adolescent female students that negativity affects their daily life activities, academic achievement and productivity. The aim of this study: Was to determine the effect of Pilates exercises on primary dysmenorrhea among adolescent female students. Subjects and Method: The study was conducted at Faculty of Nursing Tanta University Egypt. A purposive sample consisted of 100 female students who had primary dysmenorrhea and fulfilling the inclusive criteria. The students randomly allocated into study and control groups 50 students in each group. Two tools were used: Tool (I): Self-administered sheet: included three parts: (a) Bio-socio-demographic data of the students, (b) Menstrual history. Tool (II): included three parts: (a) Visual Analogue Scale (VAS), (b) Dysmenorrheal duration assessment sheet and (c) Measurement of plasma cortisol level through a venous blood sample. Results: revealed that mean scores of the students dysmenorrheal severity, duration, as well as plasma cortisol level had significantly decreased among the study group compared to the control group (P= 0.0001). Conclusion: Pilates exercises significantly decreased the dysmenorrheal intensity and duration as well as plasma cortisol level among adolescent female students. Therefore, the study recommended that Pilates exercises should be incorporated into nursing curriculum and practice as a method for relieving primary dysmenorrhea among adolescent female student.