Magnetite (Fe3O4) nanoparticles were controllably prepared by a co-precipitation approach using two precipitating agents such as sodium hydroxide and ammonium hydroxide at relatively low temperature (40 °C). The as-prepared samples were characterized by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating-sample magnetometer (VSM) techniques. The results revealed that ammonium hydroxide produced magnetite nanoparticles with smaller particle size (14 nm), compared to those prepared (22 nm) using sodium hydroxide precipitating agent. In addition, we found that the saturation magnetization of the produced magnetite nanoparticles was influenced by the obtained particle size. The determined saturation magnetization of the generated magnetite nanoparticles was found to be ca.61.3, 65.1 emu/g for those prepared using NaOH and NH4OH precipitating agents, respectively.