Metallic glasses (MGs) have recently attracted great attention in degrading azo dyes and other organic pollutants as a kind of environmental-friendly materials for wastewater remediation. In this paper, decolorization properties of MGs based on different iron-group elements (IGEs) were reported, and adsorption or reductive degradation of aqueous azo dye solutions was observed on the surface of glassy ribbons due to their different main constituents. The primary factor determining the occurrence of adsorption or degradation was considered to be the electronic nature of the MGs instead of their crystalline structures or surface states. Besides, some electrochemical information of the glassy ribbons in the azo dye solutions was also provided for understanding the mechanism of the decolorization process. Our findings suggest that such MGs based on IGEs may be good candidates for preparing tailored materials to treat azo dye solutions or other similar organic solutions. •Fe-, Co- and Ni-based metallic glasses (MGs) are designed to decolorize azo dyes.•Adsorption or degradation occurs depending on the main constituents of MGs.•Electronic nature of MGs determines whether adsorption or degradation occurs.