SUMMARY: Introduction: Chronic obstructive pulmonary disease (COPD) is a chronic progressive disease that includes chronic obstructive bronchitis and emphysema, characterized by inflammation and increased mucus production in the airways, their narrowing and destruction of the alveoli. Treatment is based on the use of bronchodilators, corticosteroids and antibiotics, and in more severe stages of the disease, oxygen therapy and non-invasive ventilation. Aim of the research: To compare the efficacy of oxygen therapy (comparison of changes in arterial blood levels pCO2, pO2, pH, SpO2 from admission to hospital discharge) between two groups of COPD patients: 1) those receiving classical oxygen and 2) those receiving non-invasive mechanical ventilation. Participants and methods: 40 patients diagnosed with COPD were divided into two groups: 1) those treated with classical oxygen therapy (n=20) and 2) those treated with NIV (n=20). The measurement devices used in data collection were acid-base status findings. Results: When comparing pH before - after therapy within group, a statistically significant difference was found in both groups (classical application: p=0.001; NIV: p< 0.000), indicating that pH values increased in both groups after treatment methods. When comparing SpO2 values before and after treatment, a statistically significant difference was found in both groups (classical application: p<0.000; NIV: p<0.000), indicating that SpO2 values increased significantly after treatment. Comparing the effect of therapy between groups on O2 elevation, there was no statistically significant difference p=0.882, indicating that there was no difference between the two methods of therapy, i.e., they had the same effect on O2 elevation in patients. When comparing the effect of therapy on CO2 reduction, no statistically significant difference (p=0.113) was found, but the results showed a much greater decrease in CO2 levels compared to baseline in the group treated with NIV, and thus the hypothesis that the use of NIV in patients with COPD reduces CO2 levels more than conventional oxygen use was confirmed. When comparing the effect of therapy on SpO2 between the two groups, no statistically significant difference was found ( p=0.833), indicating that the therapies have the same effect on blood oxygen saturation. Conclusion: The data obtained suggest that the use of NIV in the treatment of COPD is slightly more successful compared to the classical treatment with oxygen, but without statistically significant difference. Key words: Chronic obstructive pulmonary disease, non-invasive ventilation