The Semideciduous Seasonal Forest (SSF) is one of the phytophysiognomies from the Atlantic rainforest's biome, which is one of the most threatened and fragmented biomes within Brazil. In spite of that, the Atlantic rainforest possesses one of the highest degrees of biological richness and rates of endemism among worldwide biomes. The aim of this study is to diagnose and discuss the species and familie's compositions of seasonal forests in southeastern Brazil, providing subsidies for lawmakers to conserve these forests. This study took place in 4 fragments of SSF in Boituva, SP, varying in size from 17.3 to 97.7 ha. It was collected woody plant individuals with CAP (Circumference at Breast Height) of 15 cm or more within 12 plots of 100 m2 per fragment (10x10 m, total of 1200 m2 each), sampling a total of 4800 m2 area. 120 species from 43 families were sampled. From this total of species, 8 (6.7%) face some level of threat, 74 (61.7%) were defined as non-pioneer species and 72 (60%) as being animal-dispersed species. The occurrence of late and threatened tree species as peroba-rosa (Aspidosperma polyneuron Mull.Arg), jequitiba-rosa (Cariniana legalis (Mart.) Kuntze), guaranta (Esenbeckia leiocarpa Engl.), catigua (Trichilia casaretti C.DC.) and fig trees (Ficus ssp), which are barely or not sampled in the region, proves the urgency and the importance for conserving these forest fragments in Boituva, therefore contributing for regional biodiversity conservation. In conclusion, we're able to say that Boituva's SSF is relatively well preserved, since there is a great ratio of late (non-pioneer), animal-dispersed and threatened species (IUCN).