Home oxygen therapy (HOT) not only prolongs life expectancy but also improves quality of life. Serum uric acid (UA), the final product of purine catabolism, has been shown to be increased in the hypoxic state. To elucidate the prognostic significance of serum UA in patients with chronic obstructive pulmonary disease (COPD) receiving HOT, we assessed the ratio between the serum concentration of UA and creatinine (Cr) in 91 outpatients with COPD. During a mean follow-up period of 31 months, 24 patients died of acute exacerbation of COPD. The delta UA/Cr ratio was calculated as the percent changes in serum UA/Cr during HOT. delta UA/Cr was increased in non-survivors, but not in survivors, and was negatively correlated with the nadir of oxyhemoglobin saturation (r = -0.32, p < 0.01). Of the clinical and laboratory variables, only the delta UA/Cr ratio was found to be independently related to mortality by a multivariate Cox proportional-hazards analysis. The Kaplan-Meier survival curves divided into values below and above the median value (9.7%) of this ratio demonstrated that mortality was significantly higher among patients with high values than among those with low values (log-rank test: p < 0.05). We conclude that the delta UA/Cr ratio appears to be a reliable marker of prognosis, and may be useful for the long-term follow-up of outpatients with COPD receiving HOT.