Abstract: Objective:To evaluate the mechanism and the effects of breathing Helium-oxygen （heliox） mixtures on bronchial asthma.Methods:Self-control study was adopted. Seven mongrel dogs were randomly ventilated either with Air （FiO₂ 0.21） or with heliox mixtures （FiO₂ 0.21） for 20 mins. Respiratory mechanical parameters and artery blood gas were taken at the end of 20 mins period. Further more, each dog was challenged by an Ascaris antigen for 10 mins, then was randomly ventilated either with Air （FiO₂ 0.21） or with heliox mixtures （FiO₂ 0.21） for 20 mins. The same parameters were taken at the end of every 10 minperiod. On the basis of the animal experiment, we used the Heliox mixtures to three ventilated chronic obstructive pulmonary disease （DOPD） patients. Results:（1）Heliox mixtures can reduce airway resistance, peak airway pressure and work of breathing in non-challenged dogs and in antigen challenged dogs. （2）Heliox mixtures can also reduce airway resistance, peak airway pressure and mean airway pressure in three ventilated COPD patients. （3）Heliox mixtures can decrease CO₂ retention in antigen challenged dogs and COPD patients.Conclusion:Heliox mixtures can be used in the treatment of bronchial asthma, especially for patients with CO₂ retention.