Abstract: The present study aimed to determine the composition and structure of the fringe and inland mangroves near the mouth of the Amazon River in Marajó Island. We established five study sites and, in each site, we established a fringe zone and an inland zone. In each zone, we delimited five 400-m2 plots, and we selected arboreal individuals with a minimum height of 1 m. The individuals were grouped into diameter and height classes and basal area, and we analyzed five phytosociological parameters. The composition, richness, density, diversity and dendrogram analysis used were compared between the sampled fringe and inland zones. In our exploration, 344 individuals were recorded, distributed in 10 species, suggesting that Marajó Island has one of the most diverse mangrove forests ever recorded in the world. We also recorded three typical species of mangrove, namely, Rhizophora racemosa, Avicennia germinans, and Laguncularia racemosa. We also observed that the Marajó mangroves have species that occur in other ecosystems (e.g., várzea and igapós), such as Paeonia officinalis, Phalaris aquatica, and Virola surinamensis. We observed that no significant variation between zones was found in terms of richness and density. The NMDS explained variance of 95.3% but no clear pattern of dissimilarity was observed between fringe and inland. In cluster analysis, four groups were statistically well supported, with an explanation of 85% on the dendrogram. These characteristics are important for conservation policies and specific management plans for the mangroves in Salvaterra, since, just as the vegetation is unique in this region Ver menos