By means of selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM), we have studied the structure of a new ordered cuprate with a composition close to Sr 3 Ca 3 Cu 6 O 1 5 ± δ , which was found in a superconductive specimen prepared by a high-pressure technique. It was confirmed that this phase has a unique wavy modulated superstructure, with lattice parameters a a c , b 6a c and c 6a c , where a c is the cubic perovskite parameter. A revised structural model based on the two-dimensional ordering of Sr and Ca atoms is proposed, where Cu atoms are located in both CuO 5 -pyramidal and CuO 4 -square-planar coordinations.