Medicinal plants are non-timber forest products with great potential in the Sustainable Forest District of BR-163. In order to understand the productive chain from extractive medicinal plants marketed at emporiums, fairs and public markets of districts of this area, semi-structured interviews with 20 vendors of medicinal plants were carried out. Species richness was estimated by Bootstrap and similarity among the districts studied was analyzed by Sørensen's Index. 46 medicinal plants belonging to 42 genera and 21 botanical families were identified. Fabaceae, Anacardiaceae and Bignoniaceae were the most representative botanical families. The expected richness for the sample was 50 species and additional collecting would increase by at least four items the general list of richness. Santarém, Itaituba and Altamira share a larger number of species and the first is shown to be a diversified center of medicinal products, presenting the largest number of exclusive occurrences (14). The fairs and public markets are an important link of this distribution system, and should be included in government actions concerning public policies for health.