This study deals with various sedimentological aspects of the marine sediments from the bays of Nice and Villefranche-sur-Mer. Field work was conducted in November 1976, February 1977 and February 1978. The data collected includes 90 surface sediment samples and 11 cores varying in length between 20 and 60 cm. Grain size measurements were made on the total non-decarbonated sediment. The principal results obtained in the course of these investigations are the following: — The sediments are a mixture of: terrestrial detrital components and marine bioclastics. — Five principal biocoenoses represented both in the bays of Nice et Villefranche (SFBC, HP, DC, VTC and VB). — Grain size facies have been defined by submitting the weight %-values of each fraction to a "cluster analysis" or "correspondence analysis". The facies correspond more or less to those defined on the basis of the biocoenoses. Thus, there is a direct relationship between biocoenose and grain size facies.