Eighty-nine samples have been collected for ostracods, from the stratotypes for the upper part of the Moulin Liénaux Formation and the Grands Breux Formation, in the Frasnes railway section. Forty-seven taxa were recognised, of which 20 have been recorded for the first time in the Middle Frasnian (Devonian) of the Dinant Synclinorium (Belgium). The stratigraphic distributions of a series of already known species are stated more precisely. The investigated part of the section belongs to the Favulella lecomptei Zone. A new species, Bairdiacypris breuxensis nov. sp. is described. The ostracods present in the upper part of the Moulin Liénaux Formation and in the Grands Breux Formation belong exclusively to the Eifelian Mega-Assemblage and their distribution is principally controlled by the energy of the environment, linked to sea level fluctuations.