Introduction and research objective: Chronic obstructive pulmonary disease (COPD) is a heterogeneous condition characterized by airway obstruction resulting from changes in lung parenchyma and airways, and it is among the leading causes of morbidity and mortality worldwide. The aim of this study is to analyze the effect of pulmonary rehabilitation on respiratory muscle strength and to assess the impact of respiratory muscle strength on the functional capacity and quality of life of COPD patients. Participants and methods: Data were collected from the Hospital Information System regarding patients with COPD who attended the pulmonary rehabilitation program at the Clinic for Pulmonary Diseases Jordanovac, University Hospital Center Zagreb, from January 2021 to December 2022. Specialist findings, medical histories and physiotherapy records were reviewed. The data used in the study included inspiratory muscle strength (PImax), expiratory muscle strength (PEmax), results of the six-minute walk test (6MWT), and CAT questionnaire before and after pulmonary rehabilitation. Results: The study sample consisted of a total of 71 participants, including 38 males (53.5%) and 33 females (46.5%). The results showed a statistically significant improvement in inspiratory and expiratory muscle strength after the pulmonary rehabilitation program. However, the correlation between respiratory muscle strength and functional capacity and quality of life did not reach statistical significance. Conclusion: This study concluded that pulmonary rehabilitation has a positive effect on inspiratory and expiratory muscle strength. The association between respiratory muscle strength and functional capacity and quality of life did not reach statistical significance in this study, possibly due to some of the study's limitations.