Abstract:Objective: To identify antiviral activity of Toddalia asiatica against influenza virus type A in vitro. Method: More than two hundreds Chinese medicinal herb extracts were screened for antiviral activities against influenza A/PR/8/34 (H1N1) virus using 3-(4,5-dimerthylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay for virus induced cytopathic effect (CPE) in a primary screening. Positive samples were picked up and were subjected to quantitative real-time polymerase chain reaction (PCR) to quantify reduction of H1N1 virus genomic RNA. Result: Toddalia asiatica showed potent antiviral activities against H1N1 virus, with 50% effective concentration (EC50) value of 4.7 mg·L-1 in MTS assay and 0.9 mg·L-1 in quantitative PCR assay respectively. The cytotoxicity test of Toddalia asiatica generated a CC50 value of 187.2 mg·L-1 and a selective index (SI) larger than 206 in quantitative PCR. Although the best antiviral activity of Toddalia asiatica was observed with co-treatment of influenza virus infection, it remained effective even when administrated 24 h before and after the initiation of infection. Conclusion: The results suggested that Toddalia asiatica compound extract could be a candidate for anti-HlNl virus agent in the treatment of influenza.