Objective:To explore anti-reispiratory syncytial virus(RSV) effect of Chinese medicinal Reduning injection in vitro. Method:The technique of cell culture and MTT with ribavirin as positive control to observe anti-reispiratory syncytial virus effect. Results:This drug was found to be a potential inhibitor of RSV in a concentration-dependent manner with the median toxic concentration(TC50) of 3.972 g/L in Hep-2 Cell culture. The median effective concentration(EC50) was 0.428 g/L-1 when drug was added 24 h before infection. The EC50 was 1.160 g/L when drug was added 2 h after virus infection,and it was 1.189 g/L as the drug was added after it mixed with virus 24 h. The therapeutic index(TI) was 9.28,3.42 and 3.34 respectively. Conclusion:Reduning injection has the direct deactivation and blocking effect on RSV. The preventive effect is the most evident in three drug deliveries drug with the same concentration in virto.