Abstract: OBJECTIVE To study the antiviral activities of 30% EtOH-sinked polysaccharide I， 50% EtOH-sinked polysaccharide II and 70% EtOH-sinked polysaccharide III which are extracts of different parts of Radix Isatidis， D101 macroporous resin water-eluted part IV， 10% EtOH-eluted part V， 30% EtOH-eluted part VI， 50% EtOH-eluted part VII which from the water extract of Radix Isatidis， and compound slariciresinol-4， 4'-bis-O-β-D-glucopyranoside (CB) VIII and isolariciresino IX on influenza A virus A/PR8/34(H1N1).METHODS The anti-influenza A virus A/PR8/34(H1N1) in vivo experiment was applied. And the antiviral activities of extract parts and monomeric compounds were tested by measuring lung index and lung index inhibition rate. RESULTS II， III， IV， V， VI， VII， VIII and IX could obviously prolong the living time of mice infected by influenza A virus， and the results showed marked differences compared with control group (P<0.05). II， III， IV， V， VI， VII， VIII and IX could decrease the death rate of infected mice; at the meantime， II， VI， VII and VIII could also obviously reduce lung index (P<0.05)， and the lung index inhibition rates were 31.4%， 28.5%， 30.5%， and 34.0% respectively.CONCLUSION The extract II-IX of Radix Isatidis can protect the mice infected by influenza A virus， and CB may be the effective and index component with antiviral activity in Radix Isatidis.