It was established that the change in the structure of the amorphous metal alloy (AMA) as a result of heat treatment of the amorphous metal alloy Al87Gd5Ni4Fe4 at T=645 ±1 K significantly affects the decolorization of the dye Basic Blue 6/Mendola Blue (BB6/MB) at pH=1.7±0.3. The MB solution with a concentration of 4.39 μM was decolorized by 99 % within 27 hours, in the case of annealed AMAs for 30, 45, 60 min., which is 3.8 times more effective than in the case of as-cast AMAs. A change in the AMA structure due to annealing was established by X-ray analisys; kinetic analysis was performed based on experimental data and the kinetic parameters (kobs, t1/2, ksa, etc.) of the MB decolorization reaction were calculated. The surface of AMAs after reaction with aniline dye MB and the proposed scheme of decolorization of aniline dye MB using AMAs Al87Gd5Ni4Fe4 were suggested.