The direct impregnation approach is used to synthesize nickel dimethylglyoxime (NDG) on γ-alumina (γ-Al2O3) composites to be used as a catalyst. The structural, thermal, and magnetic characteristics of γ-Al2O3, NDG, and NDG/γ-Al2O3 composites are investigated and their photocatalytic performance towards methylene blue (MB) and methyl orange (MO) is examined. The fnding supports the use of NDG over γ-Al2O3 as catalysts, besides their enhanced thermal stability. The scanning electron microscope (SEM) and transmission electron microscopy (TEM) demonstrate that the catalyst particles are dispersed uniformly, indicating that the Ni microcrystalline or Ni nanoparticles on γ-Al2O3 are most likely distributed in a single phase and/or in a homogenous route. X-ray difraction (XRD) results together with the results of SEM and TEM indicated that NDG/γ-Al2O3 nanocomposite catalysts can be prepared efectively by impingement approach. The average crystallite size of γ-Al2O3 is 6 nm, whereas the average crystallite size of NDG/γ-Al2O3 composites is 10 nm. Both γ-Al2O3 and NDG/γAl2O3 composites have a weakly diamagnetic response, whereas NDG exhibits poor ferromagnetism response. The calculated values for the photodegradation efciency, after UV–visible irradiation for 130 min, towards MO dye employing γ-Al2O3, NDG, and NDG/γ-Al2O3 composites as a catalyst are 74.2, 36.7, and 61.7%, respectively, whereas their values towards MB dye are 17.8, 5.3, and 19.1%, respectively. Furthermore, when NDG was combined with γ-Al2O3 to form NDG/γ-Al2O3 composites, the degradation performance was signifcantly improved and could be suitable for the degradation of other dyes.