A microbe of Streptomyces werraensis TT 14, which was newly isolated from soil, decolorized the model melanoidin prepared from glucose and glycine, the decolorization rate being 64% in the optimal medium of pH 5.5 (2.0% starch, 1.0% yeast, 0.3% NaCl, and 0.3% CaC03) and 45% in a synthetic medium. There was virtually no difference in the UV-VIS absorption spectra of the microbially treated melanoidin and the control. The peaks of the gel permeation chromatogram for the treated melanoidin and for the control showed the same retention times, but lower molecular weight compounds increased in the decolorized melanoidin. The Cu(II)-chelating activity of the decolorized melanoidin was reduced to about half that of the control. The melanoidin component of pI 2.5 was increased and that of pI 3.5 was reduced by the microbial treatment.