We report the synthesis conditions and magnetic properties of Pt and iron oxide (Pt–FexOy) hybrid nanostructures. The injection time and temperature of the Fe precursor after the decomposition of the Pt precursor are found to be the key parameters for the tuning of FePt to Pt–FexOy nanoparticles. The particle shape can be controlled from spherical to cubic by selective molar ratios of surfactants and solvents. A comparative study of the dynamic and static magnetic properties of Pt–FexOy and FexOy, (after etching of Pt) is presented. The effective anisotropy of Pt–FexOy is found to be one order of magnitude higher than that of etched FexOy. Consequently, a strong enhancement of the blocking temperature is observed which is attributed to the enhanced interfacial anisotropy between Pt and FexOy layers.