Abstract: Objective: To evaluate the effects of breathing helium oxygen (heliox) mixtures on COPD patients suffering from hypercapnia. Methods: Seventeen COPD patients were randomly divided into treatment group (breathing heliox, 8 cases) and control group (breathing N₂-O₂, 9 cases), and the FiO₂ were in order of 21% O₂, 40% O₂, 60% O₂ and 80% O₂ respectively. Results: The data of pulmonary function tests, arterial blood gas values of the patients were recorded. The results showed that heliox reduced the breathing load, ameliorated oxygen diffusion and CO₂ eliminating obviously, but the effective duration was very short after stopping of heliox breathing. The range of heliox effective treating concentration was 40%~79% He.Conclusion:The study demonstrated that heliox breathing may be one of effective ways in severe COPD patients, and the assisted respirator of recycled helium using may save helium distinctly and maybe a useful instrument for pulmonary obstructive diseases.