Background: To evaluate the risk of transmission of vector-borne diseases transmitted by mosquitoes, regular updates of the geographic distribution of theses vectors are required. Therefore, a study base on the abundance, richness and diversity of mosquitoes was conducted between December, 2013 and November 2014 at Cotonou, the economic capital of Benin republic. Method: A cross seasonal entomological study on larvae and adults of mosquitoes was carried in fourteen (14) locations randomly at Cotonouin Peri-Urban (PU) and urban areas (UA). The study was based on sampling mosquito immature stages (larvae/pupae) from domestic, peri-domestic and natural water sources and reared to adults. Additional adults mosquito were collected by Human Landing Catches (HLC), Indoor Pyrethrum Spray Catches (PSC), Biogents (BG) sentinel traps and Windows traps (WT) in PU and UA in order to assess the richness of mosquito fauna in this city. Results: Adult’s mosquitoes from larvae collected in our study sites showed thirteen species of mosquitoes (including 3 Anophelesspecies, 5 Culexspecies, 4 Aedesspecies and 1 Uranotaenia species) belonging to 4 genera. However, when the adults came directly from HLC and the different traps cited above, 15 species of mosquitoes including 3 Anophelesspecies, 5 Culexspecies, 2 Mansonia species, 4 Aedes species and 1 Uranotaenia species belonging to 5 genera (Culex, Aedes, Anopheles, Uranotaenia and Mansonia). The abundance of the mosquito genera recorded at PU and UA varied significantly (p<0.05), with the Culex genera recording the highest abundance. Moreover, the mosquito species recorded at PU regardless the collection methods was higher significant than those obtained at UA (P< 0.05). Conclusion: The presence of Culex, Aedes, and Anopheles species highlighted by this study in the city of Cotonou is posing a serious epidemiological concern to the inhabitants of this city. Therefore, larviciding of breeding sites before the onset of the rainy season and public enlightenment on the environmental factors and/or human activities that encourage mosquito breeding are recommended