Fe3Ｏ4 nanoparticles were successfully synthesized from an aqueous Fe (OH)2 colloid under nearly neutral condition by oxidizing it with H2Ｏ2. The m orphology, structure, and magnetic properties were characterized and measured by transmission electron microscopy (TEM), x-ray diffraction (XRD), vibrating sam ple magnetometer, and superconducting quantum interference devices (SQUID). The TEM image shows that the sample consists of well-dispersed spherical particles with diameter about 18nm, and has a cubic spinel structure according to XRD. The mssbauer spectrum at room temperature is fitted using two sextet spectrum cor responding to Fe ions at A site and B site, and the results show that th e hyperfine field of the sample is a little smaller than that of bulk value, and crystalline defects exist in the sample. The saturation magnetization of the sa mple fabricated by using H2Ｏ2 is 67×10-3A·m 2/g, and the Ver wey transition was observed at 20K, but the magnetization of the sample fabricat ed by coprecipitation is only 46×10-3A·m2/g when the app lied field is 1 Tesla, and the Verwey transition was not observed in our temperature range of measurement. In addition, the superparamagnetic blocking temperature of the s ample fabricated by coprecipitation was observed at 178K.