Nannopetersius mutambuei, new species, is described from the Inkisi River basin (Lower Congo, Democratic Republic of Congo). It is distinguished from its congeners by the following combination of characters: 28-30 lateral line scales; 5 1/2 - 6 1/2 scales between lateral line and dorsal-fin origin; caudal peduncle longer than deep (length 135.7-151.7 % of its depth); 21-23 branched anal-fin rays; 10-13 gill rakers on ceratobranchial of first branchial arch; snout length 26.6-29.2 % HL; eye diameter 31.7-39.6 % HL and a black longitudinal band present in preserved specimens but absent in living specimens.