Ezhu Intravenous Injection (EII) in treating respiratory syncytial virus (RSV) pneumonia was studied. 45 patients in therapeutic group were treated with 0.04% EII in dose of 20 ml/kg/day for 7-14 days. 20 patients in the control group were treated with Huayu decoction, its efficacy on RSV pneumonia has been confirmed. The results showed that all the patients of both groups were cured and there were no statistic differences in the average days of clearing up the temperature, dyspnea and wheezing (P > 0.05). Experimental studies showed that the isolation rate of RSV on the 5th and 8th day in the therapeutic group were lower than that of infected and glucose control groups. The difference was significant (P < 0.001 and P < 0.0001). Pathological examination showed that on 5th day in infected and control group there were epithelial damages and bronchial lumen obstruction, peri-bronchial and periseptal edema, eosinophilic leucocytes and inflammatory infiltrations. The endothelial cells of alveolar capillaries swelled, platelet aggregations and thrombi occurred in its lumens. On 8th day the platelet aggregations diminished, but cellular infiltrations and damages of bronchial epithelium still existed. In therapeutic group on 5th day most of the alveolar capillary endothelial cells were normal with mild edema only. The platelet aggregation were much less than the infected and control groups. No peribronchial and peri-septal edema was observed. The results of both clinical and experimental studies showed that EII had good therapeutic effect on RSV pneumonia with no adverse reaction.