there have been ethnoveterinary reports from around the world investigating plant usage in therapeutic protocols; however, there is no information regarding the ethnoveterinary practices in brazilian amazonia. the objective of this work was to register and document the ethnoveterinary knowledge of the inhabitants of the island of marajó, eastern amazonia, brazil. in the study, interviews were conducted with 50 individuals, with the application of semi-structured questionnaires that were quantitatively analyzed using descriptive statistic methods of frequency distribution. use-value was calculated to determine the most important species. samples of plants that were reported to have medicinal value were collected and identified by botanical classification. fifty plants, distributed among 48 genera and 34 families, were indicated for 21 different medicinal uses. the family asteraceae had the largest number of reported species; carapa guianensis aubl., copaifera martii hayne, crescentia cujete l., caesalpinia ferrea mart., chenopodium ambrosioides l., jatropha curcas l. and momordica charantia l. were species with highest use- value. the plant parts that were more commonly utilized for the preparation of ethnoveterinary medicines were the leaves (56%), bark (18%), roots (14%), seeds (14%) and fruit (8%). with regard to usage, tea was reported as a usage method by 56% of the informants; most preparations (90.9%) utilized only a single plant. in addition to medicinal plants, informants reported using products of animal and mineral origin. the present study contributed to the construction of an inventory of marajó island's ethnoveterinary plants, which might be the basis for future scientific validation studies.