Co0.2Cu0.03Fe2.77O4 nanoparticles with different morphologies have been synthesized directly via a simple hydrothermal method. The effects of pH value, precursor concentration, reaction temperature and surfactant on the particle size were discussed. X-ray diffraction analyses showed that the as-synthesized Co0.2Cu0.03Fe2.77O4 nanoparticles possessed typical spinet structure. Scanning electron microscope images showed different morphologies of the particles, including truncated octahedron and octahedron. It was indicated that well-dispersed Co0.2Cu0.03Fe2.77O4 nanoparticles can be synthesized at pH values ranging from 11 to 13, and reaction temperature of 160 degrees C. The particle size decreased from 18 to 10 nm after the addition of sodium dodecyl sulphate at the pH value of 9. The magnetic measurement showed that the as-prepared Co-Cu spinet ferrite nanoparticles possessed hard magnetic property. (C) 2010 Elsevier Ltd. All rights reserved.