The Atlantic Forest is one of the richest and most threatened biomes in Brazil. However, the structure and floristic composition of many of its remnants are still unknown. This study assessed the structure and tree composition of the Serra da Tiririca – SET coastal remnant, is the largest remnant in Serra da Tiririca State Park – PESET (Atlantic Forest, RJ). In ten 50 × 20 m plots installed between the edges and the interior of the remnant, we registered 403 trees distributed in 29 families, 59 genera, and 126 species. The richest and most abundant families were Fabaceae, Myrtaceae, and Meliaceae, while the most representative species were Gallesia integrifolia towards the interior of the remnant and Piptadenia gonoacantha towards the edges. The remnant had an average Shannon-Wiener Diversity of 3.69, a total basal area of ​​19.3 m2/ha, and an average diameter and height of 20.42 cm and 11.8 m, respectively. This study shows that the SET remnant is floristically heterogeneous and has distinct structural characteristics and stretches in different successional stages related to edge and interior gradients. Anthropogenic pressures on the remnant are likely to persist and are evidenced mainly by the forest structure.