Abstract Surface structures and the electronic properties of submonolayer sulfur dioxide SO 2 molecularly absorbed on ultrathin Pd films grown on Ni(111) have been investigated by means of S K-edge surface extended X-ray absorption fine structure and near-edge X-ray absorption fine structure (NEXAFS). On the 1.2 ML Pd film, SO 2 was found by polar-angle dependent NEXAFS to be adsorbed with the molecular plane nearly parallel to the surface. This configuration is quite similar to that on Ni(111), but shows a clear contrast to the SO 2/Pd(111) case where the molecule was adsorbed with its molecular plane normal to the surface. As the Pd-film thickness increases, SO 2 gradually stands up on the surface. On the 6 ML Pd film, the surface structure of SO 2 is essentially the same as that on Pd(111). These results indicate drastic perturbations in the electronic and chemical properties of the thin Pd film compared to that of the bulk.