Abstract: In this investigation, biostratigraphica stud has been done in the filysh formation which is cropped out between Orhouye-Memlik villages (NW Ankara) based on Nannoplankton. In this studied area, two stratigraphic sections were measured and seventyumples were collected lithologically by sandstone, sandy siltstone, siltstone, claystone and marl. In the samples, sixty-five Nannoplankton species have been determined and Lithraphidites quadratus Zone has been distinguished. This zone is shown, the Uppermost Middle Maastrichtian and Upper Maastrichtian age.