Objective To observe the anti-influenza effect of a Chinese medicinal herb-Antiviral Agent No.1. Methods To study t he anti-viral effect of Antiviral Agent No.1 by means of the technique of cel l culture and using Ribavirin as a positive control. Results In MDC K cu lture, Antiviral Agent No.1 was found to be a potential inhibitor of influenza A 3 virus in a concentration-dependent manner, with a TC50 of 60.53 mg*m l-1. When drug was added 2 hours post virus infection, the EC50(TI) was 5.14 mg*ml-1(11.78); while drug was added 2 hours before infection, t he EC50(TI) was 5.20 mg*ml-1(11.65). Conclusions Antiv iral Agent No.1 had a significant anti-influenza effect on type A3 in MDCK.