In order to find less toxic antiviral agents from basidiomycetes, EA, the water soluble substance, was isolated from the carpophores of Elfvingia applanata (Pers.) Karst. Anti-encephalomyocarditis (EMC) virus activity of EA was examined in Vero cells by plaque reduction assay in vitro. And the combined antiviral effects of EA with interferon (IFN) alpha and gamma were examined on the multiplication of EMC virus. EA exhibited a concentration-dependent reduction in the plaque formation of EMC virus with 50% effective concentration ($EC_{50}$) of 2.12 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 showed potent synergism with CI values of 0.40~0.60 for 50%, 70% and 90% effective levels, but that with IFN gamma showed antagonism with CI values of 2.16~2.83.