Methylelaiophylin isolated from Streptomyces melanosporofaciens was selected as an ${alpha}$-glucosidase inhibitor with an $IC_{50}$ value of 10 ${mu}M$. It showed mixed-type inhibition of ${alpha}$-glucosidase with a $K_i$ value of 5.94 ${mu}M$. In addition, methylelaiophylin inhibited the intracellular trafficking of hemagglutinin-neuramidase (HN), a glycoprotein of Newcastle disease virus (NDV), in baby hamster kidney (BHK) cells. Methylelaiophylin inhibited the cell surface expression of NDV-HN glycoprotein without significantly affecting HN glycoprotein synthesis in NDV-infected BHK cells.