EA, the water soluble substance, was prepared from the carpophores of Elfvingia applanata (Pers). Karst. Anti-influenza A virus (anti-Flu A) activity of EA was examined of Vero cells by plaque reduction assay in vitro. And the combined antiviral effects fo EA with interferon (IFN) alpha and gamma were examined on the multiplication of Flu A with 50% effective concentration ($EC_50$) of 1.50 mg/ml. The results of combination assay were evaluated by the combination index (CI) that was analysed by the multiple drug effect analysis. The combination of EA with IFN alpha on Flu A showed more potent synergism with CI values of 0.50~0.52 of 50%, 70%, 90% effective levels than that with IFN gamma with CI values of 0.82~0.99.