A novel biosynthesized nanocatalyst, iron oxide-loaded manganese dioxide nanocomposites (Fe3O4-MnO2 NCs), was fabricated with the aid of a Perilla frutescens leaf extract. The MnO2 is composed of numerous nanoflakes radiating from the center, which results to a flowerlike structure. A change in the flowerlike morphology of MnO2 in Fe3O4-MnO2 NCs was observed due to the distribution of Fe3O4 nanoparticles on the surface of MnO2. To check the catalytic performance of the synthesized NCs, they were utilized as a catalyst for the decolorization of rhodamine B (RhB), reduction of 4-nitroaniline (4-NA), and spa C-H functionalization of 2-methylpyridines to isatins for the-synthesis of azaarene-substituted 3-hydroxy-2-oxindole derivatives. The Fe3O4-loaded MnO2 exhibited enhanced catalytic ability over MnO2. Moreover, the nanocomposites could be recovered by a magnetic separation technique and reused for five consecutive reactions without significant loss of catalytic ability. (C) 2016 Elsevier Inc. All rights reserved.