The intense anthropization of the Sanaga basin requires an acceleration of research on biodiversity and the conservation of its aquatic resources. In this framework, the ichthyofauna of the Mpem and Djim National Park (MpDNP) has been inventoried for the first time. The fish were sampled from 2017 to 2021 using diverse experimental fishing gears. A total of 79 species classified into 39 genera, 14 families, and 8 orders have been identified in the MpDNP. This ichthyofauna represents 46.7% of the 169 freshwater fish species known in the Sanaga basin. It contains 15 (62.5%) of the 24 endemic species reported in this basin, among them two Endangered and three Vulnerable species known on the IUCN Red List. Furthermore, two non-indigenous species have been inventoried. Siluriformes (36%) and Characiformes (22%) are the most represented in the MpDNP. It is suggested that the issues for conservation in this park must be focused as a priority on 15 endemic species, which may be ranged into two national protection classes A (5) and B (10), then on those in class C, which will be identified posteriorly as supplementary priorities for the offset of the residual impacts of the Nachtigal upstream hydropower plant development.