Oxide-rich planar faults with a rock-salt-type structure in perovskite grains are the prevailing type of planar defects in CaO-excess nonstoichiometric CaTiO3. These so-called Ruddlesden-Popper (RP) faults form random network structures or ordered polytypes, depending on the processing parameters. The structure and chemistry of single RP fault was observed by high-resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). The achieved point-to-point resolution in HAADF STEM imaging was below 0.2 nm. In Z-contrast imaging, it was possible to resolve 15% of the difference in the average atomic number (Z) between two adjacent atomic columns. HAADF STEM images clearly indicate that the RP fault comprises of Ca ions at the fault.