[en] Magnetic Fe₃O₄-chitosan nanoparticles were prepared by the covalent binding of chitosan (CTS) onto the surface of magnetic Fe₃O₄ nanoparticles which were prepared by hydrothermal method using H₂O₂ as an oxidizer. Transmission electron microscopy (TEM) showed that Fe₃O₄ particles and Fe₃O₄-chitosan nanocomposites were regular sphere with a mean diameter of 23 nm and 25 nm, respectively. X-ray diffraction patterns (XRD) indicated that the magnetic Fe₃O₄ nanoparticles were pure Fe₃O₄ with a spinel structure and the coating of chitosan did not result in a phase change. The coating of CTS onto the Fe₃O₄ nanoparticles was also demonstrated by the measurement of thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectra. Magnetic measurement revealed that the saturated magnetization of the Fe₃O₄-chitosan nanoparticles reached 21.5 emu g^-1 and the nanoparticles showed the characteristics of superparamagnetism