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The Campanian-Maastrichtian (C-M) rocks exposed at the Southern Galala Plateau, North Eastern Desert of Egypt are represented by Sudr Formation, which consists of snow white chalky limestone, rich in planktonic and benthonic foraminifera. The major C-M transgression resulted in a deposition of Sudr Formation in outer neritic environment with high diversity and abundance of species, which led to defining nine planktonic foraminiferal zones and establishing the stage boundaries. In comparison with the foraminiferal zones of the GSSP of the C/M boundary, the lowest occurrence of Rugoglobigerina scotti is here considered to be the only marker for this boundary. In contrast, the other species (e.g. Contusotruncana contusa) that used to define this boundary at the GSSP is a diachronous and not save to depend on it in definition of the C/M boundary. Therefore, the present study helps in refinement of the C/M boundary definition not only in the study area, but also elsewhere.