A new preparation of 1,5-benzodiazepine derivatives has been achieved in good to excellent yields by the condensation of o-phenylenediamine with a variety of ketones employing nano-γ-Fe2O3–SO3H as catalyst under microwave irradiation and solvent-free conditions. Recyclable nano-γ-Fe2O3–SO3H provided high reactivity and was easily separated from the reaction mixture by using an external magnet. The advantages offered by this method are based on the principles of ‘green chemistry’: a facile and rapid reaction, no solvent, easy separation of products and good to excellent yields..