Resumo. The function of Biodiversity Corridors is to maintain and restore connectivity between forest fragments remains. Santa Maria Biodiversity Corridor, in PR state, aims to connect Iguaçu National Park to the riparian forest of the Itaipu reservoir, through the implementation of reforestation areas between remnants of Seasonal Semidecidual Forest. This study aimed to evaluate the diversity of tree species and the floristic similarity between the areas of native secondary forests and reforested areas of different ages. There were compared the density values, diversity, evenness, and floristic composition from five study areas, and the similarity was evaluated by Jaccard and Bray-Curtis distance. In two hectares, we found 2,328 individuals of 134 species and 39 families. The floristic similarity grouped the native secondary forests, which are best preserved, and the reforested areas in different groups. The 11 exotic species found in reforested areas were not observed in the most preserved areas. So, the managament of them should be encouraged in order to protect the remaining Seasonal Semidecidual Forest.