Objective: To study the ultrastructure changes of PS system in asthma. Methods: The present study was designed to observe the ultrastructure of PS system in asthmatic guinea pig with electron microscope histochemistry. Results: Structure impairment of PS system was observed when asthma attacked. It showed that the alveolar lining layer was discontinuous, lamellar bodies and plasmosomes in type Ⅱ pneumonocytes vacuolated, and a few of them were even necrotized and disrupted into the alveolar space. Conclusion: The results indicates that the impairment of PS system might play an important role in pathogenesis of asthma.