A stable heterogeneous organotin catalyst has been prepared by in situ tethering organotin compounds on SBA-15. This was verified by XRD, TEM, N-2 adsorption/desorption at -196 degrees C, FTIR and diffuse reflectance UV-vis spectral techniques. This material was much more active than the sample prepared by the grafting method for the direct synthesis of dimethyl carbonate (DMC) from methanol and CO2 despite that its catalytic activity was dependent on the organotin amount. This could be attributed to the formation of organotin clusters with different structures and the larger surface area. After immobilization on the SBA-15 mesoporous material, the six-coordinated organotin clusters showed higher activity, compared to the tetrahedral Sn species. With increasing reaction temperature and CO2 pressure, the catalytic activity considerably increased.