In Brazil, the number of floristic inventories involving ferns and lycophytes in the Cerrado domain is considerable. However, most of the diversity is recorded for states in the Central-West Region. In addition to the Cerrado domain, Maranhão State contains part of Amazonia and a small portion of the Caatinga. However, for this state, ferns and lycophytes are poorly sampled in floristic studies and data related to the diversity of these species are insufficient. Due to the scarcity of data about these groups, conducting floristic inventories in the state is extremely important, mainly in protected areas that contain regional vegetation near primary vegetation. Thus, the objective of the present study was to conduct a floristic inventory of the fern and lycophyte species in Chapada das Mesas National Park. We identified 86 species: 69 species of ferns, distributed in 35 genera and 17 families; and 17 species of lycophytes, distributed in five genera and three families. Among the species identified, five are new records for the Northeast Region of Brazil, twenty-one are new records for Maranhão State and eleven are new records for the Cerrado; until now, these were only recorded for Amazonia and the Atlantic Forest. The most representative families were Pteridaceae with 14 species, Selaginellaceae with 12 species, Thelypteridaceae with 11 species, and Anemiaceae, Hymenophyllaceae and Dryopteridaceae with six species each. The rupicolous life form was predominant. The new occurrence records for the Cerrado, Northeast Region and Maranhão are evidence that floristic research of ferns and lycophytes is still insufficient in these areas, and a greater sampling effort is needed to increase what is known about the diversity of these plants.