The layered perovskite structures of NaYTiO 4 and homologous acid exchange form were investigated via powder X-ray diffraction and high resolution transmission electron microscopy. The NaYTiO 4 layered structure differs from the previous investigation of Blasse et al., by the incorporation of perovskite-like 2 octahedra thick lamellae instead of 1 octahedron thick lamellae and by a stacking of slabs which is primitive instead of I-centered with an (a+b)/2 gliding. The exchange of Na + cations was performed in an acid medium. This experiment suggests that half of the Y 3 + ions occupy the perovskite like cavities whereas the Na + cations are localized in the interlayer space. Consequently, this structure is probably closer to TlBa 2 CaCu 2 O 7 family compounds than to A n + 1 B n O 3 n + 1 Ruddlesden-Popper type structure with n = 1.