A new species of Euphorbiaceae from the Brazilian Amazon, Pera eiteniorum Bigio & Secco, is described and illustrated. This species is closely related to P. tomentosa (Benth.) Müll. Arg., P. membranacea Leal, and P. heteranthera (Schrank) I. M. Johnst., but can be distinguished from them by the following characteristics: the abaxial leaf surface with stellate trichomes and the blade midvein with stellate-lepidote trichomes, staminate flowers with the calyx glabrous or rarely with sparse, sericeous trichomes, and a well-developed rudimentary pistillate flower with a lageniform (flask-shaped) ovary, triangular stigma, and narrowly oblanceolate staminode. Affinities of the new taxon are discussed, and a key to morphologically similar species from Amazonian Brazil is presented.