Red mud modified by an acid digestion and alkali reprecipitation approach was employed as support for the preparation of Ni/MRM catalysts using the homogeneous precipitation method. The textural and structural properties of the as-received red mud (RM), the modified red mud (MRM) and the as-prepared Ni/MRM catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), thermogravimetry-differential scanning calorimetry analysis (TG-DSC), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDX) and N₂ sorption techniques. The analysis results revealed a mesoporous nanocatalyst system with high surface area and uniform pore-size distribution. The results of the catalytic activity measurements showed that these mesoporous nanostructured Ni/MRM catalysts were very active for ammonia decomposition. The catalyst with 15% Ni loading and calcined at 600 °C exhibited the highest catalytic activity. Due to its unique properties and the feature of resource utilization of industrial solid waste, MRM holds great promise for developing catalysts and catalyst supports for applications in various catalytic reactions including catalytic ammonia decomposition.