Propimelodus caesius is described as a new species of Pimelodidae from the main channels of the Amazon River and its large tributaries. This common yet rarely seen species is distinguished from its closest relative, P. eigenmanni, by its relatively larger eye, toothed metapterygoid bone, greater number of vertebrae, narrowly spaced anterior nostrils, and violet to blue color. Additional anatomical details are described for the diagnostic palatine bones of Propimelodus. Derived features of the basipterygium, nuchal plates and posterior cleithral process are introduced that further help to distinguish and place Propimelodus among pimelodids.Species novum: Propimelodus caesius Parisi, Lundberg & DoNascimiento