Department of Chemistry, Payame Noor University, 19395-4697 Tehran, I. R. of Iran E-mail: hassaniir@yahoo.com Department of Chemistry, Payame Noor University, Mashhad, I. R. of Iran Manuscript received online 27 September 2019, accepted 01 October 2019 Carboxylic acid functionalized organo silan on ferrite-silica nanoparticles were prepared in four steps: (i) preparation of colloidal iron oxide magnetite nanoparticles (Fe3O4 MNPs), (ii) coat silica on Fe3O4 MNPs (Fe3O4@SiO2 MNPs), (iii) functionalization of organo silan of (3-aminopropyl) trimethoxy silane on ferrite-silica nanoparticles (Fe3O4@SiO2@PA) and (iv) incorporation of carboxylic acid as a functional group on the surface of ferrite-silica-organo silan nanoparticles (Fe3O4@SiO2@PA@COOH). The properties of prepared magnetite nanocomposite were characterized by infrared (FT-IR), vibrating sample magnetometer (VSM), X-ray diffraction analysis (XRD), thermal gravimetric analysis (TGA), Energy-Dispersive X-ray (EDX) and scanning electron microscopy (SEM) spectroscopy. The prepared magnetic catalysts (Fe3O4@SiO2@PA@COOH) showed high catalytic activity for the synthesis of diindolyl oxindoles by the coupling of indole and isatin compounds with good to high yields in aqueous medium.