The novel synthetic procedure for wustite nanoparticles with cubic shape was developed in the presence of a large amount of oleylamine and oleic acid against Fe precursor. The pretreatment under reduced pressure at 130 degrees C facilitated the formation of rather larger particles, 82 nm, by removing vapor during the reaction. The oxidation of FeO to Fe3O4 was precisely controlled so that the magnetic properties could be changed from paramagnetic to ferrimagnetic with the adjustment of the reaction time.