Chapada das Mesas National Park (CMNP) is the fourth largest conservation unit in Maranhao state and an important area for the study of bryophytes due to its geomorphological characteristics, predominant vegetation, and water potential. The aim of our study was to investigate the richness and composition of leafy liverwort species in CMNP, discuss the importance of this area in the state, and present an updated checklist of the leafy liverworts for Maranhao. Our botanical material was collected during four excursions to the park. The checklist was mainly based on literature reports. Forty-one species and two varieties in eight families and 20 genera were identified in CMNP. From the state of Maranhao, 106 species and two varieties in nine families and 39 genera are reported. Our survey of bryophytes in CMNP resulted in the first records from Maranhao of 19 species. Lejeunea juruana Gradst. & M.E.Reiner is also newly found in the Northeastern region of Brazil and in the Cerrado domain. Keywords Biodiversity, bryophyte flora, conservation units, Marchantiophyta, taxonomy