The equilibrium isotherm and the breakthrough curve for adsorption of Hg(II) on polyaminated highly porous chitosan beads (PEI-CS) were compared with those for Unicellex UR-120H which was the best commercial chelate resin for removal of Hg(II) in Japan. As the intraparticle effective diffusivity Deff in PEI-CS was about two times larger than that in UR 120H, and adsorption capacity Hg(II) on PEI-CS was also larger than that on UR-120H, adsorption of Hg(II) on PEI-CS appeared feasible technically. The intraparticle concentration profiles of Hg(II) were measured for different period of time using X-ray micro-analyzer. The value of Deff was almost constant at 4 Re′ 7, and the mean value was 3.86 × 10−12 m2/s. The value od Deff increased in proportion to the influent concentration of Hg(II) Co,Hg. The pore diffusivity and surface diffusivity were determined using Deff based on the parallel transport model of surface and pore diffusions. The result showed that both the pore and surface diffusions of Hg(II) in PEI-CS particle were significant.