Novel organic-inorganic nanocomposites based on magnetite nanoparticles and konjac glucomanan (KGM) were prepared using KGM as template, FeCl 3 ·6H 2 O, FeCl 2 ·4H 2 O, and NH 3 ·H 2 O as the starting materials. The morphology and phase structure of asprepared nanocomposites and pure magnetite nanoparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The existence of KGM impacted the morphology and size of the particles. The sample demonstrated a typical ferromagnetic behavior from magnetic measurement, and the procedure we reported here is green and environment-friendly compared with common previous protocols. These Fe 3 O 4 nanoparticles and KGM/Fe 3 O 4 nanocomposites are expected to be applied in fields such as magnetic separation, electron-magnetic shielding, and so on.