Chronic Obstructive Pulmonary Disease (COPD) is a public health problem worldwide. It is a polygenic disease and a classical example of gene-environment interaction. Of the many inhalational exposures that may be encountered over a lifetime, only tobacco smoke and occupational dusts and chemicals (vapors, irritants, and fumes) are known to cause COPD on their own. Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) may be impaired in patients with COPD. Aim of the study: to assess respiratory muscle function in male COPD patients by measuring MIP and MEP values and  to identify possible correlation between MIP and MEP and the anthropometric parameters as well as degree of airflow obstruction among COPD patients. Subjects and methods: A case-control study was carried out on 50 COPD male patients and 50 of age and sex matched healthy subjects as a control group. All participants were subjected to assessment of respiratory muscle (RM) strength by MIP and MEP, pulmonary function tests {flow/volume spirometry, and MVV}, as well as the functional exercise capacity (6MWT) and the anthropometric measurements. Results: the values of MIP and MEP in COPD cases were lower than those of the control group with a statistically significant difference. In COPD cases the MIP and MEP were positively correlated with VC%, FEV₁\FVC, FEV₁%, FVC%, PEF%, MVV%, and 6MWD (p<0.00). Furthermore, COPD patients were subdivided according to the presence of respiratory muscle (RM) affection into two subgroups: Group A (patients with RM affection) and Group B (patients without RM affection). There was a significant difference between the two subgroups concerning smoking index , disease duration, VC% , FVC% ,FEV₁\FVC, FEV₁%, PEF%, MVV%, and 6MWD  (P< 0.05). Conclusion: RM is affected in patients with COPD. Measurement of MIP and MEP indicates the state of RM which is related to smoking index, disease duration, and spirometric-indices (VC%, FVC%, FEV₁\FVC, FEV₁%, PEF%, and MVV %). Recommendation: Health care workers involved in the diagnosis and management of COPD patients especially those with severe airflow obstruction should consider the possibility of RM deterioration and should have an  access to RM function assessment.