Introduction: Vitamin D deficiency is prevalent among patients with chronic obstructive pulmonary disease (COPD) and comes to be more frequent with increased disease severity. We aimed to assess the role of vitamin D supplementation in patients with severe COPD. Patients and methods: We studied 30 patients with severe COPD and vitamin D deficiency. All patients received oral vitamin D3 50,000 IU once weekly for 8 weeks, followed by a daily dose of 800 IU thereafter. Pulmonary function tests, six minute walk test (6MWT), maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), C-reactive protein (CRP), and serum vitamin D level were assessed at the start of the study and 1 year later. The frequency of exacerbations was recorded a year before and a year after vitamin D supplementation. Results: The mean serum vitamin D level was 11.80 ± 2.40 ng/dl and reached 55.30 ± 5.65 ng/dl a year after vitamin D intake (p < 0.001). We found a significant improvement in dyspnea scale (p < 0.003), 6MWT (p < 0.001), MVV (p < 0.001), MIP (p = 0.006), MEP (p < 0.001), coupled with a decrease in disease exacerbations (p < 0.001) and CRP (p < 0.001) a year after vitamin D replacement. However, the FEV1 and FVC did not differ significantly. Conclusion: Vitamin D replacement improved dyspnea, physical performance and decreased the frequency of exacerbation in severe COPD patients with vitamin D deficiency.