In the Republic of Guinea (West Africa), the diversity and distribution of striped grass mice of the genus Lemniscomys is poorly known. In the course of long-term field surveys from 2003 to 2011, we collected 97 specimens from various regions of Guinea with the aim of characterizing the morphological and genetic diversity of the genus in the country. We performed an integrative study that allowed us to detect the existence of at least two species in the collected specimens. Two molecular clades, corresponding to different karyotypes, were recovered. By comparison with type specimens and using classical morphometric analyses, we are able to confirm the presence of L. linulus and L. striatus in Guinea. We redescribe the skull and dental characters of the poorly known L. linulus and report its standard karyotype formula (2N = 56, NFa = 66). We did not collect any L. zebra in Guinea despite its presence in South Mali. In conclusion, the distributions of L. striatus and L. linulus described for Guinea and, including the previously reported L. bellieri, three species are now known to occur in this country. We recognise these three species as valid pending further revision of the genus at a pan-African scale.