A new reduced tantalate, Na2Ca2Ta3O10, with layered perovskite structure was synthesized by an intercalation reaction from the parent sodium compound, NaCa2Ta3O10, The crystal structures of these compounds were determined by the Rietveld analysis of powder X-ray diffraction pattern. Although the framework of the perovskite layer of intercalation compound is analogous to that of the parent compound, the coordination of interlayer sodium ion in the intercalation compound is clearly distinct from that of the parent compound. The sodium ions within the interlayer of intercalation compound have a rock-salt coordination because of a too strong repulsive force fas a tetrahedral coordination. The intercalation compound, Na2Ca2Ta3O10, is the first example of a reduced! tantalate with a Ruddlesden-Popper type structure.