BACKGROUND/AIM: Progressive fibrosing interstitial lung disease (PF-ILD) refers to a group of chronic lung conditions commonly associated with immunoglobulin G4-related disorders. It is characterized by progressive scarring (fibrosis) within the pulmonary interstitium, resulting in respiratory failure and early mortality. Some patients do not respond to standard therapeutic interventions. Numerous studies have confirmed the anti-inflammatory and antioxidant properties of molecular hydrogen in various disease models. CASE REPORT: In this report, we present a case study of an 85-year-old female diagnosed with suspected IgG4-related PF-ILD complicated by hospital-acquired pneumonia. On the fourth day of hydrogen-assisted therapy, a noticeable improvement in lung infiltrations was observed in chest X-rays as the patient gradually progressed towards weaning off mechanical ventilation. To assess treatment responses, we compared immune phenotypes before and after hydrogen treatment. A marked increase was observed in resting regulatory T cell levels after treatment, accompanied by a notable decrease in Fas+ helper T cell and cytotoxic T cell subtypes. CONCLUSION: This case study highlights the effectiveness of hydrogen-assisted therapy in managing PF-ILD complicated by pneumonia, warranting further research in the future.