Introduction: In post-COVID era we still have questions about the long term changes in the lung function and blood gas analysis of patients especially after severe form of Covid-19 pneumonia. The aim of this study is to evaluate those parameters and to investigate the recovery time of the patients. Methods: Patients underwent the following examinations between the second and sixth month after discharge: pulmonary function tests, blood gas analysis, and 6MWT. Results: 35 patients after severe form of Covid-19 pneumonia participated in the study. 57% of them had arterial hypertension, and the average BMI was 34. The most significant deviations were observed in the diffusion lung capacity with the main parameter - DLco. Decreased DLco<80% was observed in 73.5% of the patients. Subjectively, after submaximal effort, patients scored a mean value on the modified Borg scale, which corresponds to mild to moderate dyspnea. 25.7% of patients still had severe dyspnea after exercise. No significant correlation was found between DLco values and Borg scale score. A 6-minute walking test was performed to assess functional capacity and dyspnea. Oxygen saturation at rest was normal and after 6MWT it decreased to 89.5±3%, without significant desaturations and with a subsequent rapid recovery. However, the blood gas analysis showed normal pH and pCO2 values, but there was still a significant decrease in the PaO2 in 50% of patients. Conclusion: Recovery of diffusion capacity after disease is slow, and on the 6th month after discharge, the majority of patients still have reduced values. Although the saturation of all patients at rest remained normal, blood PaO2 values were significantly reduced in half of them.