A novel magnetic nanocomposite of g-Fe2O3 nanoparticles decorated multiwalls carbon nanotubes (MWNTs) was synthesized for the first time by a simple chemistry precipitation method. The structure and morphology of the composite was characterized by X-ray powder diffractometer (XRD), TEM and EDS. The results of XRD and TEM show that g-Fe2O3 nanoparticles is immobilized on the side wall of the MWNTs, the size of most of the particle is o5 nm.The EDS analysis shows that the atomic ratio of Fe to O is 2:3. The magnetization curves of the MWNTs and g-Fe2O3 decorated MWNTs were measured by VSM at room temperature, which indicate that the saturated magnetization (Ms), remanence (Mr) and coercivity (Hc) of the decorated MWNTs are much larger than those of MWNTs, and the decorated MWNTs exhibit well magnetic properties.