The molluscan fauna of southwestern Brazilian Amazonia is poorly known due to the lack of focused collection areas in the region since the early 20th century. The present study provides an inventory of the terrestrial gastropods from a forest fragment in the eastern Acre state, Brazil: the Humaitá Forest Reserve (“Reserva Florestal Humaitá”). Live specimens and empty shells were collected between August 2018 and January 2019. A total of 20 species were identified, distributed in 11 families. Most (13) of these species were recorded in Acre for the first time. Furthermore, we confirm the occurrence of Systrophia helicycloides (d’Orbigny, 1835) in Brazil, reiterate the synonymy of Plekocheilus pentadinus (d’Orbigny, 1835) with P. floccosus (Spix in Wagner, 1827), and synonymize Solaropsis peruviana Haas, 1951 with S. juruana Ihering, 1905.