Kemmenau is a municipality in the district of Rhein-Lahn, in the Rhineland-Palatinate, in western Germany.

It belongs to the association community of Bad Ems-Nassau.

Although Kemmenau is already mentioned in 1320, and is maybe even some centuries older, the village became a municipality only between 1816 and 1821.

Also remarkable are the prehistoric traces discoverable immediately behind the village, the still easily recognizable Roman Limes and a prehistoric circular entrenchment on the 'First'.

The name of the town derives, perhaps, from "Kemmenate", which would refer to a fortified house on the old road from Bad Ems into the Westerwald.