Synodontis ngouniensis, new species, is described. It is endemic to the Ngounié River (Ogooué River basin) and the Nyanga River basin. It is distinguished from all other Synodontis species of the Lower Guinea Ichthyofaunal Province by: a dorsal spine with a smooth anterior margin except for the presence of 1-4 feeble serrations on the distal part; a maxillary barbel with a smooth membrane, which is proximally at least as broad as the barbel thread and situated on the posterior basal two third of the barbel; 12-19 mandibular teeth; 10-13 gill rakers on the ceratobranchial of the first branchial arch; a triangular humeral process, and a striking colour pattern of black overall background colour with irregular whitish lines and dots.