Core-shell nanoparticles are highly functional material having potential applications in biomedical and pharmaceuticals due to its excellent properties like increased thermal and chemical stability, dispersibility, less cytotoxicity and biocompatibility. Fe3O4@ZnO core-shell nanoparticles were synthesized with different molar ratios of core to shell by the two-step synthesis of phyto and hydrothermal synthesis using Azadirachta indica (neem) leaves. Synthesis of nanoparticles using plants is mostly preferable nowadays owing to its eco-friendly, simple, cost-effective and biocompatible nature. The synthesized core-shell nanoparticles were identified and nanostructural properties were studied by X-ray diffractometer (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscope (SEM) techniques with EDX and Transmission Electron Microscope (TEM). Thermal stability of nanoparticles was obtained from Thermo Gravimetric Analyzer (TGA). The toxicity of the Fe3O4@ZnO core-shell nanoparticles against Vero cells was investigated using MTT assay shows that the cell viability decreases with the higher concentration of nanoparticles. (C) 2017 Elsevier B.V. All rights reserved.