The composition and morphology of surface films formed on molten magnesium in atmospheres containing SO2 were examined by XRD, SEM, EDS, AES and XPS. The results show that the surface film with a network structure was composed of MgO. MgS, and MgSO4 and had three layers: an outer MgSO4 layer, a middle MgSO4 and MgO layer and an inner MgO and MgS layer. The thickness and elemental concentration of the films varied with the SO2 content in the atmosphere, the oxidation time, and the temperature. The formation of MgSO4 can promote the growth of the film, and the SO2 content in the atmosphere and temperature could influence film growth by affecting the formation of MgSO4. (C) 2012 Elsevier B.V. All rights reserved.