Elevated inflammatory markers and muscle wasting were common in chronic obstructive pulmonary disease (COPD) patients. The purpose of this study was to investigate the effect of 7-day beta-hydroxy-beta-methylbutyrate (HMB) supplementation on inflammation, protein metabolism, and pulmonary function in COPD patients in an intensive care unit. Thirty-four COPD patients who required mechanical ventilators were randomly assigned to HMB (n=18) or control (n=16) groups. The HMB group received HMB 3 g/d for 7 days. White blood cell count, C-reactive protein, and creatinine were significantly lower, while cholesterol and total protein were significantly higher after HMB supplementation. The body weight remained unchanged in both groups. Ten subjects (55.6%) in the HMB group and 4 subjects (25.0%) in the control group had improved pulmonary function, indicated by their ventilator modes. This short-term study suggests that HMB supplementation may have anti-inflammatory and anticatabolic effect and improve pulmonary function in COPD patients in an intensive care unit setting.