This is the account of the species of Polygonaceae registered for the Serra dos Carajás, Pará state. Two genera and five species have been reported from the canga: Coccoloba coronata, C. mollis and C. parimensis, Polygonum acuminatum, and P. hydropiperoides, while, in the forest, Ruprechtia brachysepala Meisn. has been reported. Descriptions, illustrations, keys and comments are provided.