The Caatinga is a bioma with restricted occurrence to Brazil, and in spite of its socioeconomic importance and of being submitted there are a lot of decades the intense and predatory exploration of its natural resources it is not very protected and studied. This way to increase the knowledge about this bioma a phytosociological analysis of the shrub-trees vegetation was carried in the Seridó Ecological Station, Serra Negra do Norte-RN. It was sampled all individuals with a stem diameter at soil level ≥ 3 cm and total height ≥1 m, present in 30 plots of 200 m 2 area, distributed in the southeast part of the Station and with distance to each other superior to 50 m. It was 2,448 individuals registered, distributed in 22 species, 20 genera and 12 families. The density was of 4,080 individuals.ha -1 and basal area of 17.50 m 2 .ha -1 , while the heigh and diameter medium was 2.45 m and 6.80 cm, respectively. The families with larger number of species was Caesalpiniaceae with five and Euphorbiaceae with four, while in relation to the number of individuals stood out Euphorbiaceae with 855, Caesalpiniaceae with 517, Apocynaceae with 375 and Mimosaceae with 341. The diversity index H' is 2.35 nats.ind -1 and specie richness index is 2.88. The species Caesalpinia pyramidalis Tul. (catingueira), Aspidosperma pyrifolium Mart. (pereiro) and Croton sonderianus Müll. Arg. (marmeleiro) was more important in the population answering together for 58.66 % of the individuals number, 65.19 % of the basal area and 51.85 % of the importance value.