Saxatilomys paulinae, a new genus and species of murid rodent in the Dacnomys Division is described. It is based on two whole specimens and 14 individuals represented by fragments recovered from owl pellets. The samples come from the Khammouan Limestone National Biodiversity Conservation Area in Khammouan Province in central Lao PDR. This tower karst landscape is part of the Quy Dat limestone massif, which extends eastward into north-central Vietnam (Binh Tri Thien Province). The new genus and species is morphologically (and probably phylogenetically) allied to species of Niviventer and Chiromyscus, which are also members of the Dacnomys Division, but its semispinous dark gray upperparts, dark frosted gray underparts, large, extremely bulbous footpads, and a combination of derived and primitive cranial and dental traits exclude it from membership in Niviventer, Chiromyscus, or any other described genus of Indo-malayan murid. The new species is likely petricolous, and is part of a small but unique community of small nonvolant mammals containing the petricolous gymnure, Hylomys megalotis, and hystricognath, Laonastes aenigmamus. All three species have been collected only in forested, rocky habitats of the Khammouan Limestone, but comparable environments in the adjacent Vietnamese portion of the Quy Dat limestone massif may harbor these same species specialized for living in forested, karstic landscapes.