Abstract Background: Chronic Obstructive Pulmonary Disease (COPD) is characterized by air flow limitation and mucus hypersecreastion. Aim of Study: The present study was conducted to inves-tigate the efficacy of inspiratory muscle training versus expiratory muscle training on thickness fraction in patients with chronic obstructive pulmonary disease. Material and Methods: Forty patients (men) with chronic obstructive pulmonary disease were included in this study, their age ranged from 40-50 years; they had Body Mass Index (BMI) ranged from 18.5-29.9 (kg/m2). Patients were selected from outpatient clinic Faculty of Medicine, Cairo University, They were assigned randomly into two equal groups: Group Expiratory Muscle Training (EMT) which received expiratory muscle training by Positive Expiratory Pressure device (PEP) in addition to routine physiotherapy program according to department protocol in form of, percussion, vibration, shaking and postural drainage. Group Inspiratory Muscle Training (IMT), whom received inspiratory muscle training by inspir-atory trainer in addition to the same physical therapy program that applied in group (EMT), both groups received treatment program 3 times/week for 12 weeks. The variable that used on this study is diaphragmatic thickness fraction measured by ultrasonography, was assessed before and after treatment program in both groups. Results: The results revealed that there was no-significant improvement in diaphragmatic thickness fraction in two groups after twelve successive weeks, also revealed no significant difference when compared the two groups after treatment. Conclusion: Within the limitation of the present study it could be concluded that EMT and IMT results in non-significant improvement in diaphragmatic thickness fraction.