A fluorescent glucose analogue,2-[N-(7-nitrobenz-2-ox a-1,3-diazol-4-yl) amino] -2- deoxy-D-glucose (2-NBDG), which had previously been developed for the analysis of glucose uptake in living cells, was investigated to determine its biological activity on microorganisms.2-NBDG did not show any inhibitory effect on growth of yeast cells and bacteria. In contrast, 2-NBDG exhibited strong inhibitory effects on filamentous fungal growth. The growth of filamentous fungi was completely inhibited, when 2-NBDG was supplemented as sole carbon source. The inhibitory effect was decreased by the addition of glucose in the test medium. Furthermore, 2-NBDC inhibited chitinase activity of Trichoderma sp. These results suggested that the inhibitory effects of 2-NBDG on filamentous fungi might be partially due to the inhibition of chitinase.