The inhibitor of Hepatitis B virus and HIV activity according to the present invention comprises a Lentinus edodes mycelium extract obtained by the steps of inoculating Lentinus edodes fungus in a solid culture medium comprising bagasse, then disentangling the solid culture medium containing the proliferated mycelium, adding water and at least one enzyme selected from a group consisting of cellulase, protease and glucosidase to the disentangled solid culture medium with keeping the solid culture medium at 30 to 50.degree. C., grinding and milling the solid culture medium in the presence of the enzyme to obtain a Lentinus edodes mycelium extract, and then heating the extract to a temperature of not higher than 95.degree. C. to inactivate the enzyme and sterilize the extract.