This study is focused on a poorly known genus of small killifishes, Xenurolebias, comprising species uniquely living in temporary pools of the Atlantic Forest in the coastal plains of eastern Brazil (a region undergoing intense deforestation). Xenurolebias comprises two nominal, morphologically similar species, but some variability among populations suggests it represents a species complex. In order to delineate species limits, a taxonomic revision was conducted combining two different approaches: (i) a character-based approach using morphological variation (colour patterns, fin morphology, meristic and morphometric data) and (ii) a tree-based approach using mt-DNA (tRNA-Met, tRNA-Gln and ND2). The results strongly supported four species: X. myersi (Carvalho) from the Itaúnas river basin and adjacent smaller drainages; X. izecksohni (Cruz) from the Barra Seca river basin; X. cricarensis Costa, sp. nov., from the São Mateus river basin; and X. pataxo Costa, sp. nov., from the Mucuri, Itanhem and Jucuruçu river basins. Recognition of four distinct species in Xenurolebias should change views about the conservation of the species, one of which (X. pataxo) is seriously endangered and should be considered a priority for conservation.http://zoobank.org/urn:lsid:zoobank.org:pub:8485DD00-3F30-4C9F-9682-62C4718D53D9