There is no record in the literature about collections of Myxomycetes in the State of Piauí before 1997. This check-list intends to cover all currently reported taxa from savanna (cerrado), deciduous mixed forest, riverine forest, and urban zone environments of Piauí between 1998-2005. It contains a classification of the genera in order of families, followed by a list of species and lower taxa set out in alphabetical order within each genus. The three subclasses and six orders of the Class Myxomycetes are represented by eight families, 20 genera, 50 species, and two varieties. Liceaceae, represented by Licea biforis, is reported for the first time for the State of Piauí.