The core-shell type Fe3O4 nanoparticles in poly(organositsesquioxane) (Fe3O4@OcTS) were prepared by one-pot synthesis using reverse micelle method. The as-prepared ferrofluid droplets with average size 415 nm were in situ encapsulated via polycondensation Of molecularly self-assembled octenyltriniethoxysilane (OcTS). The dynamic light scattering and transmission electron microscopy investigations on coated magnetite nanoparticles revealed uniform size of spherical shape and having thin and transparent shells. These nanoparticles showed redispersibility in non-polar solvents without agglomerations due to coated by a layer of hydrophobic shells. The thermogravimetric analysis and infrared spectroscopy Suggested the existence of core-shell type. X-ray diffraction confirmed magnetite cores. The superconducting quantum interference device (SQUID) showed that they exhibited superparamagnetic behavior at 300 K and ferromagnetic at 3 K. (c) 2009 Elsevier Inc. All rights reserved.