Background: Menstrual cycle is defined as cyclic events that take place in a rhythmic fashion during the reproductive period of a woman’s life. Changes in the ovary during each menstrual cycle occur in two phases: A. Follicular phase B. Luteal phase. During the Luteal Phase Progesterone hormone level decreases which causes difficulty in breathing. Respiratory muscle stretch gymnastics which is designed to stretch inspiratory chest wall muscle during inspiration and expiratory chest wall muscle during expiration. Peak expiratory flow measurements are the most widely used tests to assess airflow limitation. Objectives: To find out immediate effect of respiratory muscle strength gymnastic on peak expiratory flow rate among young girls during their menstruation phase. Method: This study was carried out in and around Rajkot city. Subjects who fulfil exclusion and inclusion criteria were selected by purposive sampling. They were explained about the study, its usefulness and written consent were taken.30 subjects who were selected Respiratory Muscle Stretch Gymnastic Exercise was given and Pre &Post Peak expiratory flow rate was measured. Result: Pre-treatment and post-treatment Peak expiratory flow rate was analysed by Paired t-test, it was statistically significant (P value < 0.05). Conclusion: Respiratory muscle stretch gymnastic is effective in improving peak expiratory flow rate among young girls during their menstrual phase.