Harmful viruses, including dengue virus, human immunodeficiency virus, and hepatitis B virus are known to be extremely sensitive to glucosidase inhibition. Phellinus linteus, an edible medicinal mushroom, was screened as an ${alpha}$-glucosidase inhibitor. The methanol extract of P. linteus inhibited the trafficking process of Newcastle disease virus-hemagglutinin-neuramidase, a viral glycoprotein, in virus-infected baby hamster kidney cells. These results suggest that P. linteus extract inhibits viral glycoprotein expression on cell surface through inhibition of trafficking process rather than glycoprotein synthesis.