As it was previously stated by Asselberg (1971), two species of the water shrews occur in Belgium. In fact, they are not easily distinguished from each other. That is why the author studied the frequency distribution of the mandibular length and the height of the ramus mandibulae in his Neomys samples. All of them were taken from barn owl pellets originating from southern Belgium. This morphological study shows that the mandidular height is a valuable discriminant character since 99.95 % of the water shrew mandibles are higher than 4.50 mm and 99.5 of the Miller's water shrew ones are smaller than this value. The taxonomical status of the Belgian populations of N. anomalus is discussed with the clinal (N to S) size variation of this species in the mind. Finally, distribution maps are presented. The water shrew is widespread all over Belgium and Luxemburg whereas the Miller's water shrew distribution area is restricted to the Ardennes (cambro silurian and low devonian substrates) eastern of the river Meuse. The catching points of this species in Belgium are briefly described and the habitat requirements of both species commented.