The electronic bands of BaB2O4(BBO) and LiB3O5(LBO) have been computed from first principles using theabinitiopseudofunction method. Optical conductivities and densities of states in good agreement with optical measurements and x‐ray photoemission are obtained. The gap in BBO results from the borate group to the Ba. In LBO, the gap is from a fourfold coordinated borate to a threefold coordinated borate. This suggests that cluster calculations based on the borate groups alone is a reasonable approximation for LBO, but not for BBO.