ABSTRACT: For the past several decades, the Oligo-Miocene sediments of the Maltese Islands have been the subject of a variety of biostratigraphic analytical research. Recent refinement of the Mediterranean calcareous nannofossil biozonation has prompted the authors to undertake an extensive examination of 18 locations in both Malta and Gozo. Through quantitative and semi-quantitative methods, new calcareous nannofossils biostratigraphic data are obtained from the examined 147 samples collected from outcrops where the transition of the Blue Clay into the Greensand and the Upper Coralline Limestone is exposed. The new data provide a substantial improvement to the knowledge of the Maltese Islands biostratigraphy, considering that previous calcareous nannofossil studies on the investigated formations were limited both geographically and in the number of samples analysed. The recognition of specific biostratigraphic events within the MNN zonation allows for the assignment of the glauconitic-rich beds to either the Blue Clay or Greensand formations and highlights the chronological extent of several hiatuses that could be related with contemporaneous tectonic activity, and other agents of erosion. MNN Zones/Subzones derived from this present study are also assigned to specific recognized beds within the same formations.