A preliminary assessment of Ephemeroptera species diversity in Angolan freshwater ecosystems is presented. The results are based on three surveys carried out between 2016 and 2018, supplemented by literature synthesis. The area studied includes headwater streams and tributaries feeding the Okavango Delta, namely the Cubango, Cuito and Cuanavale Rivers, which together produced 35 species, and those flowing into the Zambezi River system, the Cuembo, Cuando, Luanginga and Lungué-Bungo Rivers which together produced 29 species. Twenty-one species were identified from the Cubango River, a fast flowing, rocky substrate river, different in character to all the other rivers surveyed. The other rivers, which all flow over Kalahari sand substrate with dense rooted aquatic macrophytes, generally lacking rocky substrate, produced 33 species between them. Prior to this research, only one mayfly species had been described from Angola in 1959. During the 1990’s, research on the Cunene and Kavango Rivers from the Namibian side produced the first lists of shared Angolan mayfly species, which have been included in this summary. This checklist of Angolan mayfly species, including the recent expeditions plus the earlier studies, gives a current total of 71 morphologically distinct mayfly species, many new to science. The work is currently on-going and additional species are likely to be identified.