Cobalt ferrite (CoFe2O4) nanoparticles of average size 4 nm with narrow size distribution are synthesized by reverse micelle approach. The nanoparticles are characterized using powder X-ray diffraction (XRD), Dynamic Light Scattering (DLS), Theromogravimetric analysis (TGA) and Fourier Transform Infrared Transmission Spectrometry (FTIR). Three successive transformations are observed in the thermogram that correspond to the loss of solvent and surfactant: onset of the amorphous to crystallize conversion: and isochemical transformation, i.e. migration of cations between octahedral and tetrahedral sites in the inverse spinel structure. The isochemical transformation is further confirmed by FTIR. The IR absorption bands observed at 460 and 615 cm(-1) in the as-prepared CoFe2O4 nanoparticles correspond to the ferrite skeleton of octahedral and tetrahedral sites, respectively. The peak intensity at 615 and 460 cm(-1) is shifted to 601 and 440 cm(-1), respectively upon annealing at 320 and 400 degrees C. These results confirm migration of cations from the octahedral to the tetrahedral sites. (C) 2010 Elsevier B.V. All rights reserved.