Resins coated with nickel/nickel boride nanoparticles were used to remove brilliant green, methyl violet, methylene blue, phenosafranine, and brilliant cresyl blue from water. The effects of pH, adsorbent dose, contact time, and initial dye concentration on the adsorption efficiencies were investigated. The point of zero charge for the adsorbent was pH 9.5. Isotherm studies were conducted using Langmuir, Freundlich, and Dubinin-Radushkevich models, and thermodynamic studies were also performed. Adsorption of the five dyes was found to obey the Langmuir isotherm model and was endothermic. The maximum adsorption capacities calculated from the Langmuir isotherm were 66.7, 88.5, 144.9, 56.2, and 147.1 mg/g for methylene blue, brilliant cresyl blue, methyl violet, phenosafranine, and brilliant green, respectively. E values obtained from the Dubinin-Radushkevich isotherm showed that the adsorption mechanism was chemical in nature. Furthermore, three kinetic models (pseudo first-order, pseudo second-order, and intraparticle) were investigated. The pseudo second-order kinetic model fit the five cationic dyes best.