The presented experimental research focuses on obtaining iron oxide nanoparticles with high efficiency for magnetic hyperthermia treatments. They were prepared by two different synthesis methods. The first sample was prepared in the modified process of thermal decomposition of Fe precursor in a polyol solution. The second sample was prepared by coprecipitation based on mixing iron salts solution with NaOH solution. Samples were characterized by X-ray powder diffraction, SQUID measurements, transmission electron microscopy and Zetasizer Nano series. The results derived from two systems obtained by different synthesis methods represent valuable knowledge in the fundamental research on magnetic behavior of nanoparticle systems and also a significant contribution in the developing field of application of magnetic hyperthermia.