Based on herbaria specimens and especially on samples recently collected in the area, a revision of the hornwort genera Dendroceros and Megaceros in the African archipelago of São Tomé e Príncipe is presented. The four resulting species are described and illustrated, with comments on their distribution and ecology. A new species of Dendroceros is proposed, D. paivae C. Garcia, Sérgio et Villarreal sp. nov., which is distinguished by delicate thallus, long and slender capsules, distinct spore ornamentation and a particular epiphyllous ecology, growing closely adherent to living leaves. The new hornwort is rare and localized but abundant where found. Also the presence of Dendroceros crispatus Nees in Africa is confirmed. The genus Megaceros is reported for the first time from São Tomé e Príncipe, corresponding to the second report from Africa of M. flagellaris (Mitt.) Steph. A key to the Dendrocerotaceae from São Tomé e Príncipe is presented.