Nanoparticles of two composites of the Fe2O3-Ni1-xZnxFe2O4 system were synthesized by the coprecipitation method, using agitation by sonication and nitrogen bubbling. The synthesized nanocomposites were characterized by: X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Both nanocomposites presented the two crystalline phases corresponding to the rhombohedral and cubic spinel structures, characteristics of hematite and cubic ferrites. The unit cell parameter (a) of the spinel phase increases with the increment in the concentration of Zn2+ cations, indicating that an expansion of the lattice occurs. The two nanocomposites are formed by agglomerated nanoparticles, with irregular shapes and mean sizes less than 10 nm. Magnetization measurements as a function of the applied magnetic field suggest that the particles of the two nanocomposites are in the superparamagnetic regime, at room temperature.