A new perovskite, Na[Cu2.5Ti0.5]Ti4O12, has been synthesized using a conventional solid-state technique. Neutron and synchrotron X-ray powder diffraction studies in combination with density measurements and bond-valence calculations have revealed that the material crystallizes in the cubic Im (3) over bar space group (a = 7.38472(2) angstrom, Z = 2) with the square-plane site accommodating 16.7% of Ti4+. This is the highest level of non-Jahn-Teller cation substitution for Cu2+ reported to date for CaCu3Ti4O12-type perovskites prepared at ambient pressure.