In this study, colloidal solution of superparamagnetic MnFe2O4 nanostructure was fabricated in presence of carboxymethyl chitosan. Different content of polymer and manganese-iron concentrations were examined and the physical and chemical properties of magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction pattern (XRD), transmission electron microscopy (TEM) zeta-potential and vibrating sample magnetometer (VSM). XRD pattern showed the spinel structure for the both bare and polymer coated nanoparticles. FTIR spectra demonstrated that the carboxyl methyl chitosan binds to the surface of magnetic nanoparticles via a hydrogen bond and it was supposed that the mechanism of CMC stabilizing the suspension is electrostatic repulsion. Furthermore, the stability evaluation by zeta potential presented the optimum value of 50 mV for CMC concentration of 3 wt%. TEM results revealed a spherical shaped morphology with an average diameter of 9 nm and narrow size distribution for the optimum polymer concentration of 3 wt%. Both naked and CMC-MnFe2O4 nanostructures demonstrated super-paramagnetic behavior, as confirmed by zero coercivity and remanence on the magnetization loops. Moreover, the presence of low (10%) manganese content revealed the optimum net magnetization of 37.80 emu/g.