Abstract: Objective To study the antiviral effect of arbidol hydrochloride(Ahyd) on respiratory syncytial virus in vitro.Methods Multi-mode administration and multi-dose were used to investigate the mechanism of the antiviral activity.Cell survival rate of each testing group infected by the virus was measured using 3-4,5-dimethylthiazo(-2-yl)-2,5,diphenyle-tetrazolium bromide(MTT)assay,and reverse transcription PCR(RT-PCR) was applied to detect virus amount of each testing group.Results Survival rate of viral group reached to 20.2%,and that of Ahyd treated group was up to 71.8% with a linear dependent manner in the range of no-toxicity dose.Another important results showed that 2-△△Ct of viral group was 9.33 and that of Ahyd treated group was decreased to 3.21,which was equal to one third of that of viral group.Conclusion Ahyd has a significant preventive and therapeutic effect on the infection caused by respiratory syncytial virus.