The double perovskite compounds Ca 2LnRuO 6 (Ln = Y, La–Lu) have been prepared. The X-ray diffraction measurements show that Ca 2+ and Ln 3+ ions are partially disordered at the A site and half of the B site of the perovskite ABO 3, and that Ca 2+/Ln 3+ and Ru 5+ ions located at the B site are regularly ordered. Therefore, these compounds should be represented by Ca 2− x Ln x [Ln 1− x Ca x ]RuO 6. The ratio of the Ln 3+ ion located at the B site varies with its ionic radius. It is clear that the larger Ln ions occupy the A site and that the smaller Ln ions tend to occupy the B site. Through magnetic susceptibility and specific heat measurements, it has been found that Ca 2LuRuO 6 shows an antiferromagnetic transition at 14 K.