Dithizone-immobilized zeolite (DIZ) adsorbent has been prepared by mixing natural zeolite and dithizone in the toluene medium at 50 °C for 4 h to yield brown-reddish adorbent with high affinity and selectivity to Hg(II) ion. The optimum conditions for the adsorption of Hg(II) ion using this adsorbent is achieved at pH 5 and 90 min of contact time. The kinetic study suggests that the rate of adsorption of Hg(II) on DIZ is higher than that of activated zeolite (AZ). Adsorption isotherm experiment reveals that the adsorption Hg(II) on DIZ is best described by Langmuir model with adsorption capacity, equilibrium constant and energy higher than that of AZ. This higher performence of DIZ has been found to be the effect of the functional groups of dithizone immobilized on the surface of the zeolite. This modified adsorbent has been successfully applied in the removal of Hg(II) ion in the river water spiked with Hg(II) ion with satisfied results, suggesting that the modified adsorbant may be used in the future for removal of Hg(II) in industrial waste or used as promising material for solid phase extraction and preconcentration of Hg(II