The optimization of Hg(II) adsorption conditions from aqueous solutions with 3-mercaptopropyl trimethoxysilane-modified kaolin (MMK) used as a new adsorbent was analyzed by response surface methodology (RSM) approach. The MMK adsorbent was characterized by means of energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). According to the quadratic model obtained from central composite design (CCD) in RSM, the optimal conditions for adsorption were found to be 30.83 mg/L, 0.1 g, 7.44 and 31.41 A degrees C for C (o) , adsorbent dosage, initial pH, and T (A degrees C), respectively. With the obtained model, the maximum amount of adsorbed Hg(II) and %Hg(II) removed was calculated to be 30.10 mg/g and 98.01%, respectively. Langmuir and Dubinin-Radushkevich isotherms fitted well the experimental results. Thermodynamic studies revealed that the adsorption was physical, exothermic, spontaneous. The results indicate that MMK a new adsorbent has great potential for the removal of Hg(II) from aqueous media.