A fungus, Geotrichum candidum Dec 1, newly isolated as a dye-decolorizing microorganism, was used to decolorize molasses and an anthraquinone dye in shaken flasks. A degree of decolorization of molasses of 87% was achieved after 12 days of cultivation, and the maximum rate of decolorization of the dye in the culture broth was obtained in 7 days. The apparent activity of peroxidase in the molasses, which is responsible for dye decolorization, was significantly lower than that of purified peroxidase, due to the inhibition by molasses, but the inhibition was reduced after the fungus was fully grown. As two ultrafiltered fractions of molasses were similarly decolorized by Dec 1, Dec 1 apparently degraded colored substances of a wide range of molecular weights. When Dec 1 was cultivated in a medium in which sucrose in the molasses was hydrolyzed with invertase, the degree of decolorization of molasses, and rate of decolorization of the dye were similar to these obtained above.