Resumo. Phytosociology of tree vegetation in Iguaçu National Park is inserted within Atlantic Forest biome and is considered the largest Brazilian non-Amazon Park. Despite its importance and its significant forest area, there are few scientific studies related to its vegetation. In order to meet this demand, we conducted a phytosociological inventory of the tree vegetation by means of plots installed in different environments, striving to achieve optimum environmental representation. In the classification of vegetation by TWINSPAN the forests were initially separated into ambient montane and submontane. An ecotone region between seasonal and araucaria forests was observed in the montane site, at an altitude above 700 m. The semideciduous forest montane was observed at altitudes of 600-700 meters. The Forest Seasonal Submontane in the lowlands was separated into two subformations, Typical and Humid, due to physiognomic variations regulated by geomorphology and humidity. According to the results, the tree vegetation of Iguaçu National Park is a remnant of great importance for the conservation of forest species in southern Brazil, among which stand out Aspidosperma polyneuron Müll. Arg., Araucaria angustifolia (Bertol.) Kuntze, Euterpe edulis Mart. and Ilex paraguariensis A. St.-Hil.