A novel nitrate solution combustion process for formation of magnetic Mg0.5Ni0.5Fe2O4 nanoparticles was introduced, and XRD, VSM, SEM, TEM, and BET techniques were employed to characterize the nanoparticles. For Mg0.5Ni0.5Fe2O4 nanoparticles prepared at 400 °C for 2 h with 20 mL absolute ethanol, the average size and the saturation magnetization were approximately 22 nm and 8.1 A·m2/kg, respectively. Mg0.5Ni0.5Fe2O4 nanomaterials were subjected to reactive red 2BF adsorption, and the adsorption performances were investigated. The results revealed that the experimental data fit the Temkin isotherm model and the pseudo-second-order kinetics model, suggesting that the RR-2BF adsorption process was a monolayer-multilayer-associated chemisorption mechanism. The effects of pH on the adsorption capacity and cycle capacity of the magnetic Mg0.5Ni0.5Fe2O4 nanoparticles for the adsorption of reactive red 2BF were revealed.