This study aimed to determine the tree structure, floristic composition and species diversity in the Araucaria State Park, southern Brazil. We allocated 100 plots of 100 m2 (1 ha) each one, and we recorded all trees with diameters at breast height ≥ 5 cm. We sampled 1368 individuals of 106 species, 75 genera and 44 families. Fabaceae, Lauraceae and Myrtaceae showed the greatest richness of species. The diversity of tree species was high (H ‘= 3.96), although the observed richness was less than the estimated one. The basal area was 46.88 m2 ha-1. We observed an intrinsic association between Araucaria angustifolia and Nectandra megapotamica, and a predominance of secondary and zoochorous (> 70%) species. Endangered and vulnerable species in the Santa Catarina state, such as Araucaria angustifolia, Cedrela fissilis, Dicksonia sellowiana and Ocotea porosa were sampled in the Park, highlighting its importance for the conservation of the Mixed Ombrophylous Forest.
