Material collected in 1974 during the Austrian Hydrobiological Mission of F. Starmühlner to the Comoros and during recent years by one of the authors (NM) in the course of an ongoing freshwater monitoring program in Mayotte is the basis of this first larger study of the mayfly family Baetidae in the Comoros Archipelago (Comoros, Mayotte). We identified eight different species using morphological characters, four species on both the Comoros and Mayotte, three species on the Comoros only and one species on Mayotte only. Two species, Dabulamanzia mayottensis sp. nov. and Nigrobaetis richardi sp. nov., are new to science; they are described and illustrated based on their nymphs. The nymph of Afroptilum bicorne (Ulmer, 1909) is described for the first time and its assignment to this species is discussed. The description of the previously endemic Malagasy species Potamocloeon (Aquaediva) freitagae (Gattolliat, 2001), is complemented based on the additional material from the Comoros and re-examination of the type material. A key to the nymphs of all species of Baetidae in the Comoros and Mayotte is provided and the biogeography of the family in this region is discussed.