The Universidade Federal Rural do Rio de Janeiro (Federal Rural University of Rio de Janeiro) Botanical Garden (JB/UFRRJ) has a green area occupied mostly by sparsely planted arboreal species, in addition to a small area of regenerating forest and plantations. In consideration of the Brazilian federal rules for botanical gardens, the collection of the Arboretum was studied systematically: collection of complete samples, herborization and identification of the species by accepted botanical methods. The occurrence of native species from different Brazilian phytogeographic domains and common names were verified. A total of 125 species of arboreal Eudicotyledons, belonging to 30 families were registered, of which Fabaceae, Bignoniaceae, Malvaceae, Myrtaceae and Anacardiaceae were the richest ones. Species in danger of extinction and others with biological, ecological or economic value are represented, demonstrating the importance of the area to flora conservation.