A new species of Sorocea A. St.-Hil., S. angustifolia Al. Santos & Romaniuc (Moraceae), was discovered in the humid rainforests of Guapimirim, within the Parque Estadual dos Três Picos, Rio de Janeiro. The new species resembles S. bonplandii (Baill.) W. C. Burger, Lanj. & Wess. Boer by the similar shape of its staminate inflorescences but is distinguished by the leaf lamina that is narrowly oblong, to 13 cm long and to 2 cm wide. Blade margins are not spinulose, and the leaf apex is usually cuspidate to caudate; the staminate flowers have the staminal filaments basally free. The new species is endemic to the Atlantic rainforest of Rio de Janeiro State in southeastern Brazil and is critically endangered due to its restricted geographic area of occurrence: between the municipalities of Guapimirim and Cachoeiras de Macacu.