Single crystals of Nb‐Ta superlattice have been grown by molecular‐beam epitaxy. The epitaxial relations between the samples and several kinds of sapphire substrates have been determined using x‐ray diffraction. The interface region between Nb and Ta layers is estimated to be about 6 A˚. A terraced structure of the superlattice is discussed. Reflection high‐energy electron diffraction patterns of Nb and Ta surfaces observedinsitushow half‐order streaks and an elongation of lattice constant in the growth direction.