Some problems including low treatment capacity, agglomeration and clogging phenomena, and short working life, limit the application of pre-treatment methods involving zero-valent iron (ZVI). In this article, ZVI was frozen in an amorphous state through a melt-spinning technique, and the decolorization effect of amorphous ZVI on Acid Orange II solution was investigated under varied conditions of experimental variables such as reaction temperature, ribbon dosage, and initial pH. Batch experiments suggested that the decolorization rate was enhanced with the increase of reaction temperature and ribbon dosage, but decreased with increasing initial solution pH. Kinetic analyses indicated that the decolorization process followed a first order exponential kinetic model, and the surface-normalized decolorization rate could reach 2.09 L/(m2 x min) at room temperature, which was about ten times larger than any previously reported under similar conditions. Recycling experiments also proved that the ribbons could be reused at least four times without obvious decay of decolorization rate and efficiency. This study suggests a tremendous application potential for amorphous ZVI in remediation of groundwater or wastewater contaminated with azo dyes.