ABSTRACT: RationalePulmonary rehabilitation is an important treatment for patients with Chronic Obstructive Pulmonary Disease, who are often vitamin D deficient. As vitamin D status is linked to skeletal muscle function, we aimed to explore if high dose vitamin D supplementation can improve the outcomes of rehabilitation in Chronic Obstructive Pulmonary Disease. MATERIAL AND METHODS: This study is a post-hoc subgroup analysis of a larger randomized trial comparing a monthly dose of 100.000 IU of vitamin D with placebo to reduce exacerbations. 50 Subjects who followed a rehabilitation program during the trial are included in this analysis. We report changes from baseline in muscle strength and exercise performance between both study arms after 3 months of rehabilitation. RESULTS: Vitamin D intervention resulted in significantly higher median vitamin D levels compared to placebo (51 [44-62] ng/ml vs 15 [13-30] ng/ml; p < 0.001). Patients receiving vitamin D had significantly larger improvements in inspiratory muscle strength (-11 +/- 12 cmH2O vs 0 +/- 14 cmH2O; p = 0.004) and maximal oxygen uptake (110 +/- 211 ml/min vs -20 +/- 187 ml/min; p = 0.029). Improvements in quadriceps strength (15 +/- 16 Nm) or six minutes walking distance (40 +/- 55 meter) were not significantly different from the effects in the placebo group (7 +/- 19 Nm and 11 +/- 74 meter; p > 0.050). CONCLUSION: High dose vitamin D supplementation during rehabilitation may have mild additional benefits to training.