Highly dispersion stability and mobility of CMC-stabilized zero-valent iron nanoparticles were prepared by manipulating the reduction conditions of NaBH₄ at pH 8.  The improved of Fe nanoparticle stability was due to strong complexation of Fe³⁺ precursor with the carboxylate groups present in CMC in basic solution and strong interaction of CMC at the surface of Fe nanoparticles. The results from TEM clearly showed that nanoparticles are roughly spherical and appear as discrete particles with the mean particle size around 10 nm. The ability of colloidal iron nanoparticles to remain in the water and the ability to penetrate in sand was also preliminary studied. CMC stabilized iron nanoparticles remain suspended in water for more than a month and most of all particles able to pass through the column of sand.