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An efficient and convenient synthesis of 2‐substituted benzimidazoles catalyzed by magnetic Fe3O4 supported by modified bentonite (MB) was developed. Herein, a separable, magnetic catalyst Fe3O4/MB was successfully prepared on the basis of exploring Fe3O4 synthesis by co‐precipitation method. Fe3O4 was obtained in 96.09 % yield using sweet orange oil as a reducing and protecting agent. The result showed that the sweet orange oil played a crucial role in the preparation of Fe3O4. Fe3O4 and Fe3O4/MB were characterized by powder XRD, SEM, EDX, XPS and BET, and were further applied to catalyze the synthesis of 2‐substituted benzimidazoles. The applicability of the substrate was investigated on the basis of optimizing the reaction conditions. As a consequence, 2‐substituted benzimidazoles were obtained in 37.01–91.68 % yield. It suggested that Fe3O4/MB was an environmentally friendly and low‐cost catalyst possessing good catalytic activity, broader substrate adaptability and excellent recyclability. It is a promising catalyst in industrial production. [ABSTRACT FROM AUTHOR]