The structural and magnetic properties of non-coated and SiO2-coated iron oxide (Fe3O4) nanoparticles (NPs) were investigated by a polarized small-angle neutron scattering (P-SANS) method. Measurement of the P-SANS allowed us to obtain nuclear and magnetic scattering cross sections of the NPs under applied magnetic field. The analysis of the scattering intensity provided the structural parameters and the spatial magnetization distribution of the non-coated and the SiO2 coated core shell NPs. The measured radius of both NPs and the shell thickness of the core shell NPs were in consistent with those measured by the transmission electron microscopy. In comparison, the magnetic core radii of both NPs were 0.12-0.6 nm smaller than the nuclear radii, indicating the magnetization reduction in the surface region of core Fe3O4 in both NPs. However, the reduced magnetization region, which is the surface spin canting region, of the SiO2-coated NPs was relatively narrower than that of the non-coated NPs. We suggest that the SiO2 coating on the Fe3O4 NPs may stabilize the spin order of atoms and prohibit the oxidation or defect formation at the surface region of the Fe3O4 NPs, and enhance the corresponding magnetization of the Fe3O4 NPs by the reduction of the spin canting layer thickness. (C) 2015 Elsevier B.V. All rights reserved.