New compositions for perovskite-type oxides (Nd 0 . 1 5 Sr 0 . 8 5 )(Al 0 . 5 7 5 Nb 0 . 4 2 5 )O 3 (NSAN) and (La 0 . 1 5 Sr 0 . 8 5 )(Ga 0 . 5 7 5 Nb 0 . 4 2 5 )O 3 (LSGN) were investigated from solid state reactions and grown by the Czochralski method as substrates for GaN epitaxial growth. Both compounds crystallized in the cubic system. The lattice mismatch with GaN and the linear expansion coefficients were investigated. Both crystals have a fairly small lattice mismatch with GaN. Therefore, they are expected to be good substrates for the growth of high-quality GaN epitaxy.