A survey of the small mammals of Huu Lien Nature Reserve, Lang Son Province, Vietnam (21°40′52″N, 106°20′28″E) resulted in the capture of 187 specimens representing 21 species of bat, insectivore, and rodent: Suncus etruscus, Rhinolophus pearsonii, Rhinolophus pusillus, Rhinolophus stheno microglobosus, Aselliscus stoliczkanus, Hipposideros armiger, Hipposideros larvatus, Harpiocephalus harpia, Pipistrellus paterculus, Scotomanes ornatus, Callosciurus erythraeus, Dremomys rufigenis, Niviventer fulvescens, Niviventer langbianis, Tonkinomys daovantieni, Rattus andamanensis, Rattus losea, Rattus tanezumi, Mus caroli, Rhizomys pruinosus, and Atherurus macrourus. In addition Ratufa bicolor and Tamiops sp. are reported from observations. The recently described genus and species Tonkinomys daovantieni is currently known only from material collected during the present survey and is apparently endemic to karst habitats in northeastern Vietnam.