Abstract: Nanoparticles especially coated or supported magnetic metal nanoparticles, have emerged as a new class of nanocatalyst. Simple separation from the reaction mixture is one of the advantages of these catalysts. Also they can be reused several times without any reduction in the activity. These catalysts showed not only high catalytic activity but also a high degree of chemical stability in various organic solvents. Benzodiazepines constitute an important class of heterocyclic compounds which possess a wide range of therapeutic and pharmacological properties. They are widely used as anticonvulsant, antianxiety, analgesic, sedative, anti-depressive, and hypnotic agents. Owing to their versatile applications various methods for the synthesis of benzodiazepines have been reported. One of the commonly reported methods for the synthesis of benzodiazepines is the condensation reaction between o-phenylenediamines and ketones. In continuation of our interest in the application of nanocatalysts in organic synthesis, in this work, cellulose-based nanocomposite containing high contents of Fe3O4 nanoparticles used as a catalyst in the condensation reaction between o-phenylenediamines and ketones for synthesis of benzodiazepines in good to excellent yields under mild conditions. A good correlation between the amount of surface acid sites as well as the surface morphology of the catalysts and the catalytic activity has been observed. This method has been found to be eco-friendly, simple and economical. The solid supported nanocatalyst could be recycled and reused without significant loss of its catalytic activity.