The study was carried out on the gallery forest of the Bacaba stream situated in the Municipal Ecological Reserve ‘Mário Viana’ (14°43′S, 52°21′W) in Nova Xavantina, Eastern Mato Grosso, Brazil. Three sections of the gallery (upper, middle and lower) running downstream and differing in slope were surveyed by stratified sampling. Fortyseven nested 10m × 10m plots were analysed in each section, giving a total sampling area of 1.41ha overall. All trees or lianas ≥ 15cm girth at breast height were recorded and a total of 129 species belonging to 105 genera and 47 families were found. Diversity was high, with the Shannon index ranging from 3.84 nats/individual in the lower section to 4.08 in the middle section. The most important families (IVI) were Caesalpiniaceae (upper and middle sections) and Arecaceae (lower section), and the most important species were Diospyros obovata (upper section), Hymenaea courbaril var. stilbocarpa (middle section) and Mauritia flexuosa (lower section). Morisita and Sørensen indices of similarity were calculated. The floristic composition was complex and included species in common with a number of Brazilian forest types and with cerrado (savanna), as well as many widespread species, but stronger links with Amazonian forests could be detected. This is to be expected since the area lies in the ecotonal zone of the cerrado and Amazonian forest biomes and the Bacaba stream itself is a tributary of the Mortes–Araguaia–Amazon river system.