This paper presents the synthesis route, the properties of the polynaphthylamine (PNA)/Fe3O4 nanocomposites and their adsorption studies of arsenic (III) removal ITom water. Microstructure and morphology of the nanocomposites with the polymer contents of 0 percent, 5 percent and 10 percent and 15 percent have been investigated by measurements: X-ray diffraction analysis (XRD), SEM, TEM, Raman scattering spectrum. The studied results showed that the size of nanocomposite particles was about 20 nm. The saturation magnetization of the samples had values of about 45-65 emu/g as measured by vibrating sample magnetometer (VSM). The investigations of isothermal adsorption process and influences of pH to arsenic adsorption capacity showed that the nanocomposite materials with appropriate polymer components have good arsenic adsorption ability in water.