AgNPs@Fe3O4-nanostarch nanocomposite was prepared using Helicteres isora L. extract as a reducing and stabilizing agent. FESEM, EDS, TEM, FT-IR, XRD, VSM, and elemental mapping were utilized to characterize the synthesized nanocomposite. The nanocomposite was applied as a magnetically separable and reusable catalyst for the efficient preparation of various arylaminotetrazoles by reacting different arylcyanamides with sodium azide in high yields without forming hydrazoic acid. We report the oxidation of benzyl alcohol to benzaldehyde by hydrogen peroxide under solvent-free conditions in good yields using AgNPs@Fe3O4-nanostarch as a magnetically separable and reusable catalyst. The catalyst showed high catalytic performance in the reduction of 4-NP, CR, RhB and MB using NaBH4 as the source of hydrogen in an aqueous medium. The products were formed in good yields through a simple method and facile work-up. In addition, the catalyst could easily be separated from the reaction mixture using an external magnet and reused for at least 5 runs with no significant loss of catalytic activity.