Resumo. The present study aimed to raise the floristic composition and the phytosociological structure of the tree community of an permanent flooded swamp forest known as 'Floresta Padulosa' as well as its adjacent vegetation (semi-deciduous seasonal forest 'Alto Montana') in Itacolomi State Park, Ouro Preto and Mariana, Minas Gerais State, Brazil. The study site is located at an altitude of 1,350m, and the regional climate is classified as Cwb by Köppen¿s system, with average annual rainfall varying from 1.100mm to 1.800mm and the average annual temperature from 17.4 ºC to 19.8 ºC. In order to make the phytosociological survey 14 plots (10m X 30m) were located, seven in each physiognomy, and all individuals with a minimum CBH (Circunference at Breast Height) of 15cm were sampled. A total of 1136 individuals were sampled, belonging to 24 families, 37 genders and 53 species. The families with higher richness values were Myrtaceae (11), Melastomataceae (5) and Annonaceae, Fabaceae and Rubiaceae (3). The similarity among the studied fragments can be considered lower than expected, showing the existence of individual phytogeographic units, with distinct floristic characteristics. The influence of the adjacent vegetation on the swamp forest may be the most important factor in its floristic differentiation if compared to other swamps areas of Brazil.