We examined the effects of supplementary nutritional therapy (calorie:REEx1.5) for one year using branched-chain amino acid (BCAA) enriched-elemental diet in addition to usual diet in 12 malnourished patients with COPD. Improvement in nutritional status was assessed by BW, %IBW, %AMC, transferrin, and plasma amino acid BCAA. PImax was significantly increased after 3 months' therapy. Although no significant change was found in pulmonary function and arterial blood gases, subjective symptoms evaluated by D.O.E., oxygen cost score and QOL index were improved. Significant correlations were found between delta BW and delta AMC and delta TSF, delta PImax and delta AMC, delta oxygen cost score and delta PImax, which suggest that improvements in nutritional status contributed to the improvement in respiratory muscle function and subjective symptoms. These findings suggest the effectiveness of supplementary nutritional therapy using BCAA-enriched elemental diet in patients with COPD.