Five new species of the recently created genus Occidenchthonius Zaragoza, 2017 are described from caves of Portugal: Occidenchthonius alandroalensis sp. nov., O. algharbicus sp. nov., O. duecensis sp. nov., O. goncalvesi sp. nov. and O. vachoni sp. nov. The species Occidenchthonius cardosoi (Zaragoza, 2012) and Chthonius ischnocheles (Hermann, 1804) are reported from new localities in different karst units of Portugal. New morphological characters are proposed for use in the Chthoniidae taxonomy. An updated key to the genus Occidenchthonius is given.