We describe a new stiletto snake, Atractaspis, from western Liberia and southeastern Guinea. The new species shares with morphologically similar western African Atractaspis species, A. reticulata and A. corpulenta, the fusion of the 2 nd infralabial with the inframaxillary. From A. corpulenta the new species differs by a more slender body (276-288 ventrals and 19 or 20 dorsal scale rows versus 178-208 ventrals with 23-29 dorsal scale rows), a divided anal plate and divided subcaudal scales (both non-divided in A. corpulenta). The new species differs from most A. reticulata by having 19 or 20 dorsal scale rows at midbody (versus 21-23, rarely 19), and a lower ventral count (276-288 versus 304-370). The new species thus has a relatively longer tail: snout-vent-length / tail-length in the female holotype (15.7) and paratype (21.5) versus a mean of 23.6 in seven female A. reticulata. The new Atractaspis likely is endemic to the western part of the Upper Guinea forest zone and thus adds to the uniqueness of this diverse and threatened biogeographic region.