Synthesis of superparamagnetic nanoparticles of Fe3O4 was carried out via coprecipitation using NH3.H2O and NaOH solutions in Ar and N2 atmosphere. The obtained magnetic nanoparticles were characterized using X-ray diffraction, Fourier transform-infrared, scanning electron microscopy, variant strength magnetization and N2 gas adsorption–desorption techniques. The results indicated that all samples exhibit superparamagnetic properties, although the saturation magnetization of the Fe3O4 nanoparticles prepared with NaOH under Ar atmosphere was higher in contrast to other samples. The crystalline structural study of different samples of Fe3O4 nanoparticle demonstrates the magnetite crystal with a cubic spinel structure. Morphology of the particles was uniform and semispherical shape nanoparticles were approximately in the range of 15-25 nm