Introduction: Thoracotomy is a surgical procedure to gain access into the pleural space of the chest. It includes: Median sternotomy, Posterolateral thoracotomy & Anterolateral thoracotomy. The risk of post-operative pulmonary complications is relatively high following thoracic surgery; rates have been recorded at between 19% and 59%. Deep breathing exercises induce sustained increase in trans-pulmonary pressure, which increases lung volume, improves ventilation, oxygenation, prevents basal atelectasis, re-inflates collapsed lung regions, and reverses minimal postoperative atelectasis. Respiratory Muscle Training especially has been shown to improve respiratory muscle function and helps to reduce dyspnoea on exertion. Improvements in strength, speed, power and endurance leads to improvement in the performance of MIP & MEP, which in turn leads to increase in strength and endurance of the diaphragm and accessory muscles during respiration. Aim And Objective: To study the immediate effect of respiratory muscle training on peak expiratory flow rate in post thoracotomy individuals. Method: Participants were divided into two groups by random allocation. The intervention group received RMT of 2*30 repetition with standard breathing exercises whereas the control group were given only standard breathing exercises. Immediate post-test outcomes were measured on peak flow meter and Rate Perceived Exertion (RPE) as well. Result: Analysis was done in SPSS 20 Mean Age (61.93±11)). Data was not normally distributed, so non parametric test was used. According to the data there was significant statistical improvement of PEFR in thoracotomy individuals. (P≤0.002). Conclusion: There is significant statistical difference of PEFR after Respiratory Muscle Training in post thoracotomy individuals. Key words: Peak expiratory flow rate, Respiratory muscle training, Thoracotomy.