Maastrichtian to Ypresian-dated sediments from the 12 Frères borehole. (Fresco, southwestern Côte d'Ivoire), are here investigated for paleoenvironmental and paleogeographic significance. For this study, the preparation of palynological slides in the laboratory is done in three steps.: (1) sampling and physical treatment, (2) chemical attacks (HCl 10%, HF 40%) to dissolve the mineral matter and preserve the organic matter contained in the sediments, (3) mounting the collected organic matter between slide and coverslip for microscopic study. Quantitative analyses of dinoflagellate cysts and other palynomorphs have allowed reconstructions of paleoenvironments. Thus, from bottom to top, nine (9) depositional environments ranging from outer neritic to inner neritic via a lagoon or estuarine environment were determined. Following Lentin and Williams (1980), the deposits in the 12 Frères section are attributed to a tropical to subtropical province paleogeography.