Various microorganisms were screened for their ability to decolorize molasses wastewater under thermophilic and anaerobic conditions. Strain MD-32, which was newly isolated from a soil sample, was selected as the best strain. From taxonomical studies, the strain was concluded to belong to the genus Bacillus, most closely resembling B. smithii. The strain decolorized 35.5% of molasses pigment within 20 d at 55 degrees under anaerobic conditions, but no decolorization activity was observed when it was cultivated aerobically. At all the concentrations tested molasses pigment was effectively decolorized by MD-32, with decolorization yields of around 15% within 2 d, The molecular weight distribution as determined by gel filtration chromatography revealed that the decolorization of molasses pigment by the isolated strain is accompanied by a decrease in not only small molecules but also large ones.