This work concerns the Coleoptera Hydradephaga collected in several sites of the Moukalaba - Doudou National Park and in external zone North of the Park. In the Park 107 species have been collected, 109 species in external zone. The Authors describe 7 new species of Dytiscidae: Hydrovatus rigatoi n. sp. (confossus group) chiefly distinguishable for shape of penis; Bidessus mboyei n. sp. (sharpi group, ovoideus subgroup) close to B. ovoideus Régimbart, 1895 and B. seydeli Biström, 1885, distinguishable for smaller size and for shape of penis; Clypeodytes acutipenis n. sp. close to C. densepunctatus Biström, 1988, distinguishable for apex of penis clearly pointed; Laccophilus sinuosipenis n. sp. (deceptor group) close to L. bizonatus Régimbart, 1895, distinguishable for sinuous shape of penis; Laccophilus cianferonii n. sp. (deceptor group) close to L. bilardoi Pederzani and Rocchi, 1982, chiefly distinguishable for shape of penis; Copelatus bapounouensis n. sp. (erichsonii group, atrosulcatus subgroup) close to C. ellai Bilardo and Rocchi, 1995, chiefly distinguishable for shape of penis; Copelatus gigas n. sp. (erichsonii group, vigintisulcatus subgroup) close to C. fasciatus Bilardo and Rocchi, 1995, chiefly distinguishable for large size and for shape of penis. Moreover some observations concerning the ecology and data about the distribution of several species are provided.