A detailed micropalaeontological analysis with dinoflagellate cysts of the Cretaceous sections intercepted by five wells in western Belgium allows a biostratigraphical correlation and a chronostratigraphical interpretation of the sediments concerned. The transgression of the Cretaceous sediments on the southern part of the Palaeozoic Brabant Massif appears to be strongly diachronous. In the Nieuwkerke and Oostduinkerke wells, situated south of the present day topographic crest of the Brabant Massif (Nieuwpoort-Oudenaarde), the transgression is dated as Late or latest Cenomanian and close to the crest in the Keiem well as Late Turonian. North of the crest, in the De Haan and Knokke wells, it is dated as Late Santonian. The Late Cenomanian strata are present only in the Nieuwkerke and tbe Oostduinkerke wens, at some distance south of the crest. Sediments dated as Turonian are found only south of the crest, with a decreasing thickness towards the crest, from the Nieuwkerke to the Keiem well. The Coniacian also occurs only south of the crest, with a similar thickness in the two latter wells. The Santonian bas a similar thickness in the same two wells south of the crest and is present only with a reduced thickness of Late Santonian age in the De Haan and Knokke wells. Campanian sediments occur only north of the crest, in both latter wells. Only Lower Campanian is present in the De Haan well, while a more complete Campanian section, followed by Maastrichtian, is observed more to the north, in the Knokke well. A post-Cretaceous erosion is thought to be responsible for the observed thickness variations in the Campanian north of the crest