Two new double perovskite oxides, Ca2NiOsO6 and Sr2NiOsO6, have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca2NiOsO6 was found to adopt a monoclinic structure (P21/n), while Sr2NiOsO6 was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca2NiOsO6 orders in a canted antiferromagnetic state at about 175 K while Sr2NiOsO6 orders antiferromagnetically at about 50 K.