Inclusion Criteria:  Post-COVID-19 Interstitial Lung Disease (ILD) patients who had completed the treatment of acute phase and have recovered, but despite after a month from recovery diagnosed as post-COVID ILD based upon the persistent respiratory symptoms with functional impairment and radiological sequela.  At least 30 days required after discharge for hospitalized patients and isolation termination for outpatients Confirmation of the diagnosis of COVID-19 via real time polymerase chain reaction assay (rt-PCR) or antigen or antibody test in the acute phase of COVID-19. Presence of sequelae interstitial changes in follow-up thorax high-resolution computed tomography (HRCT)/CT. Presence of persistent respiratory symptoms in the post-COVID-19 period or hypoxemia at rest and/or desaturation with exercise.  Exclusion Criteria:  Patients who had a normal lung imaging examination (radiography, tomography, etc.) at discharge. Diffuse parenchymal lung disease before pandemic Cystic bronchiectasis Presence of contraindications for systemic corticosteroids (uncontrolled Diabetes, uncontrolled Hypertension, unstable angina pectoris, history of acute coronary syndrome at last month, presence of active infection, active peptic ulcer, presence of uncontrolled psychiatric disease, etc.) Decompensated heart failure Contraindications for pulmonary function tests and those who cannot cooperate with the test Younger than 18 years old Pregnant women Breastfeeding women Those who do not give written consent