Abstract: Objective To explore the effect of retinoic acid(RA)on macrophage(Ma)function in lung allergic inflammation.Methods The chicken ovalbum in was used for the establishment of sensitization model of SD rats and the rats asthma was induced with continuous inhalation of ovalbum in for 30 days.After inhalation of paraff in,RA,and RA+ glucocorticoid,light and electron micro scopic examination of the lung,thymus and spleen of all groups were conducted to observe allergic in flammation and the changes of Ma structure and function.Results The vacuolar degenerations of alveolar epithelial cell,endothelial cell and alveolar Ma were observed in para ffinoil group and RA+gluco corticoid group 30-40 days after the challenges.The number of sensitized cell was positively correlated with the number of a lveolar Ma(r= 0.933).There was Madegradation with follicular hyperplasia within spleen in paraffin oil group.There were heavier a lveolar injury and inflammation in RA+gluco corticoid group.A lveolar Ma was correlated with sen sitized cells(r=0.7)during later period in the RA+glucocorticoid group.In RAg roup,there were less alveolar damage and better ultrastructure recovery.The active phagocytosis of Ma was negatively correlated with sensitized cells(r=-0.862).There were decreased degeneration of splenic Ma and proliferation in thymus and spleen.Conclusion RA can increase the phagocytosis of Ma,reduce inhaled antigen,and protect alveolar structure.Degradation of Ma may contribute to the disorder in internal environment and mimune mibalance.