The sucking louse fauna associated with Mongolian mammals is inadequately known. We provide a list of 25 species of sucking lice recorded from Mongolian rodents including previously published records, and new records of specimens collected during an expedition to northwestern Mongolia in 2015. Hoplopleura inagakii Ono and Hasegawa and Polyplax cricetulis Chin are newly recorded from Mongolia and 2 new host associations in Mongolia are recorded for Hoplopleura acanthopus (Burmeister). We describe Hoplopleura altaiensis n. sp., from the Gobi Altai mountain vole, Alticola barakshin Bannikov (type host) with an additional specimen from Alticola strelzowi (Kastchenko) (Strelzow's mountain vole). Both sexes of the new species are illustrated with scanning electron micrographs and line drawings. We note small morphological differences in the shape of the female subgenital plate between specimens prepared for scanning electron microscopy versus those prepared for light microscopy following DNA extraction.