Cobalt ferrite (CoFe 2O4) nanoparticles were synthesized using polyethyleneglycol as surfactant in a simple reflux system and subsequently heat treated from 200°C to 800°C in N 2 atmosphere. The samples were characterized using: X-ray diffraction, Infrared spectroscopy, Scanning electron microscopy, Transmission electron microscopy, Thermogravimetry, Differential scanning calorimetry, surface area and Vibrating sample magnetometry. Nanoparticles obtained crystallize with a spinel type cubic structure and an average size between 9 and 102 nm and a surface area between 77.6 and 14.9 m 2 /g. Magnetization measurements versus applied field verified the strong influence of synthesis conditions on the particle size and therefore on the magnetic properties. The maximum field magnetization M(H) shows hysteresis loops that not saturate at the maximum field applied, reaching a maximum magnetization of 44.62 emu/g.