The adsorption of Sarin (GB), isopropyl m ethyl phosphonofluoridate (C4H10FO2P), on the surface of magnesium oxide was investigated at the B3LYP/6-31G(d) and MP2/6-31G(d) levels of theory using the representative cluster models. The geometry of Sat-in was fully optimized, while the geometry of the oxide fragment was kept frozen. The location and orientation of GB on the surface of MgO were found in cases when Sarin is physadsorbed or chemadsorbed. The adsorption results in the polarization and the electron density redistribution of GB. The interaction energies of Sarin-magnesium oxide corrected by the BSSE energy were predicted. The adsorption energy obtained at the MP2/6-31G(d) level of theory for the most stable chemadsorbed system is about -50 kcal/mol. The adsorption on the small fragment of MgO can lead to decomposition of Sarin.