Magnetic iron oxide nanoparticles are promising tools for medical applications like hyperthermia or magnetic drug targeting. The relevant properties in these applications strongly depend on particle size and size distribution. In order to investigate the influence of mean size as well as size distribution, iron oxide powders from particles by a cyclic method based on “conventional” precipitation from Fe-salt solution were prepared. Increasing mean particle size with increasing number of cycles is confirmed by XRD. Magnetic parameters of the saturation hysteresis loop, hysteresis losses calculated from minor loops and switching field distributions are shown. A fractionation experiment on a fluid sample of particles prepared by 3 cycles was carried out in order to improve the hysteresis losses.