A series of chemically active mesoporous silicas(HMSs and SBAs), which show selective adsorption properties for Hg(II) ion, has been synthesized using primary amines and poly(alkylene oxide) triblock copolymer as a structure-directing agent. This study investigated the effects of crystallinity and surface properties on the mercapto densities and the metal adsorption capacities. The steric effect of functional groups was observed in the supports with the pore diameters less than 2.8 nm, while no close correlations between the pore diameters of supports and mercapto densities of the adsorbents were observed in those with the pore diameters greater than 3 nm. The results of XRD and elemental analysis show that the pore uniformity and the crystallite domain size of the supports, which were calculated by Scherrer formula, plays a key role in the determination of the extent of the mercapto densities of the adsorbents. The adsorbents showed high selectivity to the adsorption of mercury ions in a single metal solution among others under the given conditions.