Resumo. This work aimed to evaluate the floristic composition of the remaining riparian forest of a stream called ‘Sanga Lagoão do Ouro’, seeking to obtain information about its degradation, analyzing the distribution of the species in the different floristic strata, the natural regeneration and the exotic species presence. The study was conducted at the riparian forest of ‘Sanga Lagoão do Ouro’, which is tributary of the third order of ‘Vacacaí-mirim’ River. Its spring is located in an urban area, covering several villages, the campus of Federal University of Santa Maria as well as an extensive rural area. The predominant soils are classified as: Bruno-Grayish (Bruno-Acinzentados), Red-Yellow (Vermelho-Amarelos) and Red (Vermelhos) Alfisols (Argissolos) and Udalf soil (Planossolos Háplicos), which are of low natural fertility and quite susceptible to water erosion. The floristic surveying was accomplished in 12 sampling plots of 300 m2 each, demarcated along the margin of the stream where the strata were evaluated: seedlings, natural regeneration and arboreal. The floristic survey shows degradation of the studied riparian forest, which is evidenced by the low number of native species, the poor distribution of the species in the different strata and the great presence of exotic species. The species that present the highest frequency and which appear in the three floristic strata mentioned in this study have greater for natural regeneration, such as: Eugenia uniflora, Allophylus edulis, Psidium guajava, Cestrum strigilatum, Prunus myrtifolia, Zanthoxylum rhoifolium, Casearia sylvestris, Cupania vernalis and Schinus terebinthifolius.