Interfaces in heterostructures composed of two different transition-metal oxides are now a strongly growing research topic in condensed-matter physics due to the anomalous electronic properties very different from those of the component materials. Here we present resonant soft x-ray scattering studies of SrTiO₃/LaAlO₃ superlattices. From the existence of the forbidden Bragg peak (003), we found evidence for differences between the bulk and the interface electronic structures. The photon-energy dependence near the O 1s edge and polarization dependence showed that there are two structures split by ∼ 1 eV, which were not observed in the O 1s x-ray absorption spectrum. The origin of this splitting is still unclear, but we consider that this is not only due to the splitting of t_2g states at the interface but also due to the difference between the O 1s binding energies for bulk and interface oxygen.