Inverse photoemission spectroscopy has been used to study the unoccupied electronic state of NbC and TiC (100) surfaces. Most of the features of the spectra are well explained by the unoccupied bulk states expected from theoretical band calculations along Γ-X direction. An unoccupied surface state is identified for the NbC (100) surface. After oxygen adsorption, empty O 2p derived states are observed for both surfaces. For the TiC (100)-O surface, IPES spectra indicate that the oxycarbide layer is formed by heating at 1000°C, which is not observed for the NbC (100)-O surface.