Resumo. The present work was performed in the Natural Municipal Park of Santo Ângelo (RS) owned by the City Government of Santo Ângelo, the objective was to evaluate the floristic composition and the phytosociological structure of the forest, in an area with 13 hectares. Twelve units samples of size 10 x 20 m systematically distributed in the area were used , in which these unit samples were measured and identified all individuals with DAP greater than or equal to 10 cm. The results were analyzed and processed with the use of the software FITOANÁLISE, calculating the phytosociological parameters of density, dominance, frequency, value of importance, value of coverage, diversity Shannon H¿ index and Morisita index. 35 species were found, belonging to 30 genera and 21 families, of which (Sebastiania commersoniana (Baill.) L. B. Sm. & Downs), açoita-cavalo (Luhea divaricata Mart), maria- preta (Diatenopterix sorbifolia Radlk) e canela preta (Nectandra megapotamica Spreng.) were the ones with greater in phyto-sociological parameters from the tree components of forest. The species with the greatest value of importance (VI) were açoita-cavalo (Luhea divaricata Mart) with 50,53; branquilho (Sebastiania commersoniana Baill.) with 46,24; mariapreta (Diatenopterix sorbifolia Radlk) with 26,93, canela preta (Nectandra megapotamica Spreng.) with 20 and farinha-seca (Machaerium stipitatum Vogel) with 16,64. The forest vertical structure Luhea divaricata showed higher values in the upper stratum and Sebastiania commersoniana Baill in middle and lower strata.