A heat stable protein, named GFAP, was isolated and purified from the fruiting bodies of edible fungus Grifola frondosa by a procedure of (NH₄)₂SO₄ precipitation, and ion-exchange chromatography on DEAE-Sepharose column and gel filtration on Sepharose-6B column. According to PAGE and IEF,GFAP had a single band with pI 3.67. And it consisted of two subunits of 34 ku and 40 ku when encounted by SDS-PAGE. GFAP is identified as a glycoprotein containing 2% sugar. The N-terminal amino acid sequence of the 40 ku subunit is ACCVPSVTEFENAINSDPVM,which has no homology with other sequences in GenBank. GFAP possesses the inhibitory activity against the infection of Tobacco mosaic virus. When mixed with TMV(10 mg/L) and inoculated in local lesion host,Nicotiana glutinosa, GFAP was able to completely inhibit the infection of TMV,and with TMV(40 mg/L),it still had an infection effect of higher than 60% at the concentration of 4 mg/L.