Unique magnetic properties of superparamagnetic iron oxide (hematite) nanoparticles prepared by nanocasting in a periodic nanoporous silica (PNS) matrix are described in this work. The nanoparticles were prepared via a novel approach, when the external surface of PNS was modified to become more hydrophobic. The prepared composite sample was characterized by the synchrotron related techniques small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and X-ray absorption near edge spectra (XANES) measurements, by nitrogen adsorption/desorption, and by high resolution transmission electron microscopy (HRTEM). The investigation of the magnetic properties by superconducting quantum interference device (SQUID) magnetometry at the temperatures 2−300 K shows the superparamagnetic relaxation of the particles with a blocking temperature of TB ∼32 K. Below TB, the ferromagnetic interactions are present as suggested by coercivity HC ∼1900 Oe. The value of magnetic moment mP = 296 μB of the hematite particle was estimated by distribution of Langevin functions. This magnetic moment originates in uncompensated surface spins of Fe3+ ions due to the small size of hematite particles (5 nm) and due to the loading of nanoparticles into silica matrix. The magnetic behavior of the Fe2O3@PNS nanocomposite is mainly related to the surface effects (spin canting and different surface to volume spin ratio).