Resumo. ABSTRACT The largest fragment of Figueira Farm (Londrina-PR state) with an area of 266 ha, is a Private Natural Heritage Reserve, and one of the most important remnants of the region. The aim of this study was to characterize the structure and tree diversity of this fragment, and evaluate the floristic relationship with other fragments of semideciduous forest studied in the state of Paraná. One hundred plots of 10 x 10 m were allocated and the arboreal individuals with 15 cm or more in circumference at breast height were sampled, resulting in 1,569 individuals, 32 families, 66 genera and 93 species. Families with greater number of species were Fabaceae (16 species), Meliaceae (nine species) and Myrtaceae (nine species). Trichilia clausseni C.DC. was the species with the highest importance in the study, reflecting higher values of density and relative frequency in the fragment. The largest relative dominance was presented by Gallesia integrifolia (Spreng.) Harms, by presenting large individuals with the highest values of basal area. The Shannon diversity index was found to be 3.37 nats/ind, a value considered significant and similar to other surveys in the region, and the index of evenness by Pielou was 0.743, indicating balance in the number of individuals among species. The presence of singletons and rare tree species in Paraná as well as the total diversity of species and the degree of conservation of the fragment, demonstrate the importance of the preservation and management of the remnant. Geographical proximity associated with similar environment factors as well as the predominant type of phytogeographic unit, showed closer floristic relationships, on the other hand, local environmental factors such as proximity to watercourses differentiated its flora of nearby places.