We have determined the equilibrium geometry and electronic structure of the compound, BC3 using the ab initio pseudopotential local orbital approach and the local-density functional formalism. The boron-carbon compound, BC3, is a layered material with gra- phitic structure, where every fourth carbon atom is substituted by boron. The nearest-neighbor distances are predicted to be 1.42 A for the C-C bond and 1.55 A for the B-C bond. A monolayer of BC3 is found to be a semiconductor, and the observed metallic behavior of the bulk sample arises from interactions between neighboring layers in BC3 with AA and AB stacking. Based on total-energy calculations, we find BC3 to be less stable than graphite for the structures investigated.