Two new species of Benthamia A. Rich. (Orchidaceae) from Madagascar, B. boiteaui Hervouet, sp. nov. and B. bosseri Hervouet, sp. nov., are described. Both have been found at the summit of Ambondrombe (Haute Matsiatra region, near Ambalavao), and also, for B. boiteaui Hervouet, sp. nov. in the Ranomafana national park, and for B. bosseri Hervouet, sp. nov. in the Andringitra massif. The two species are represented in the Paris herbarium at the Muséum national d'Histoire naturelle (MNHN) by specimens collected in April 1941 by Pierre Boiteau and more recently, for B. boiteaui Hervouet, sp. nov. by specimens at K, MO and TAN, and for B. bosseri Hervouet, sp. nov., by specimens collected by Jean Bosser in April 1964. With linear leaves and an elliptic dorsal sepal, B. boiteaui Hervouet, sp. nov. can easily be distinguished from other Benthamia with white flowers. The non resupinated, drooping flowers and the arching spike of B. bosseri Hervouet, sp. nov. are very distinctive too.