The Guiana Center of Endemism (GCE) extends across Guyana, Suriname, French Guiana, north of the Amazon River and east of the Negro River in Brazil, and Venezuela to the south of the Orinoco River. Regarding diversity of nonvolant mammals, the Brazilian part of this center is less studied, especially the area corresponding to the north of the State of Pará. Seven field trips lasting 12–15 days each were conducted in five conservation units in northern Pará, in order to assess the nonvolant mammalian fauna. Small mammals were captured using conventional and pitfall traps. Medium-sized and large mammals were recorded through direct observations on diurnal transect censuses, collections, camera traps, indirect evidence, and in some cases, interviews. We recorded 60 species distributed in nine orders. Among other contributions, a recently described species of Monodelphis was collected, and the range distribution of Didelphis imperfecta was extended. In addition, the night monkey Aotus sp. was recorded on the east of the Trombetas River for the first time. The high number of records for game and/or threatened species evidences that the studied area is highly preserved, and the newly created protected areas are strategic for the conservation of mammals in the GCE.