The genus Copelatus Erichson, 1832 ( Coleoptera , Dytiscidae , Copelatinae ) of Madagascar is revised in two parts. This review is restricted to the Copelatus species that have fewer than ten elytral + one submarginal stria, including all species except those of the erichsonii species group. Both morphological and molecular (mitochondrial COI) data are used in an integrative taxonomic approach. Thirteen species are recognised, of which five are described as new: Copelatus ankaratra sp. nov., Copelatus kely sp. nov., Copelatus pseudostriatus sp. nov., Copelatus safiotra sp. nov. and Copelatus vokoka sp. nov. Copelatus unguicularis Régimbart, 1903 and Copelatus apicalis Fairmaire, 1898 are both transferred to the genus Madaglymbus Shaverdo & Balke, 2008 ( comb. nov.). Copelatus mimetes Guignot 1957 is a junior synonym of the widespread Afrotropical–Arabian Copelatus pulchellus (Klug, 1834) ( syn. nov.). Copelatus marginipennis (Laporte, 1835) is reinstated ( stat. nov.) as a valid species with Copelatus aldabricus Balfour-Browne, 1950 and Copelatus aldabricus var. simplex Guignot, 1952 as junior synonyms ( syn. nov.). We designate lectotypes for Colymbetes marginipennis Laporte, 1835 and Copelatus obtusus Boheman, 1848. Copelatus peridinus Guignot, 1955 is recorded for Madagascar for the first time and Copelatus nodieri Régimbart, 1895 is rejected as a species present in Madagascar.