A facile and robust approach is presented to prepare superparamagnetic chitosan (CS) spheres by simply dropping iron ions and CS mixture solution to ammonia aqueous solution. Fourier transform infrared spectra, X-ray diffractions, and thermogravimetric analyses of the obtained spheres indicate that the composite spheres consisted of CS and Fe3O4. The microstructures of the surface and the inner part of the sphere were observed by scanning electron microscope to indicate nano scale of the Fe3O4 component. The results suggest that the nano sized Fe3O4 particles can be stabilized by CS molecules in the matrix of sphere to avoid aggregation based on their binding interaction. Because of the nano scale distributed Fe3O4 particles, the composite spheres show superparamagnetic properties, and the saturation magnetization of the composite sphere increases linearly with the Fe3O4 content. An electron probe microanalyzer was employed to measure the energy dispersive spectra of the magnetic sphere, through which the element contents at different points along the radius of a magnetic CS sphere have been obtained. It has been found that the Fe3O4 content decreased gradually from outer surface to its inner core. Moreover, the composite sphere was calcined in air at 700 degrees C to prepare spherical hollow sphere. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 3587-3594, 2012