The aim of this research is determine of adsorption ability diffusivity bentonite external mass transfer coefficient (Ks) of the mercury which transfer from the aqueous solution to the external surface of the bentonite particles determination of the effective pore diffusivity (De) to know diffusion affectivity of mercury through the pores of the solid particles adsorption of the mercury on to effective bentonite surface and determination Freundlich s equation constant. In this research variable was done initial concentration of the mercury (20.0 10.0 5.0 2.5 and 1.0 ppm) and the contact time (1.0 3.0 7.0 and 10.0 days) used to adsorption mercury on the 50 ml mercury solution with 120 mesh 0.5 g bentonite as adsorbent. The adsorption done agitation with magnetic sirrer during 3 hours. The result of this research was Ks 9.0508 x 10-8 (pangkat -8) cm/sec De 5.7051 x 10-12 (pangkat -12) cm/sec constant equilibrium Freunlich k 2.8864 n 2.5880and adsorption ability 97 15