Magnetic-nanoclay montmorillonite/iron oxide (MMT/Fe3O4) was prepared by co-precipitation method and montmorillonite/iron oxide/silver (MMT/Fe3O4/Ag) was synthesized, by chemical reduction method, by reduction in silver nitrate salt with sodium borohydride as reducing agent. The average crystal size of the nanoparticle was calculated as 15 nm from the Debye–Scherrer formula. Subsequently, montmorillonite/iron oxide/silver was used in degradation of Rhodamine B in the presence of sodium borohydride to evaluate catalytic activity of it. Optimum working conditions; the pH was 5.2, the amount of catalysis was 1.51 g/L, the dye concentration was 12 mg/L, and the amount of NaBH4 was 0.3 ml. The reduction reactions followed by pseudo-first-order kinetics and rate constant value were found to be 0.3454 min−1. COD were investigated by chemical catalysis using MMT/Fe3O4/Ag and NaBH4. Complete degradation of Rhodamine B was achieved in 8 min by using MMT/Fe3O4/Ag as catalysts, while degradation of 46% of Rhodamine B was achieved in 60 min by using MMT/Fe3O4. Graphical abstract: [Figure not available: see fulltext.]