Tonkinomys daovantieni, a new genus and species of murid rodent in the Dacnomys Division, is described. It is represented by 14 adults collected from talus habitats in the forested tower karst landscape of the Huu Lien Nature Reserve of northeastern Vietnam. The combination of semispinous, dense, grayish black fur covering upperparts; a dark gray venter; gray ears; a thick, bicolored tail considerably shorter than length of head and body; and large, extremely bulbous footpads is unlike any other species of Indomalayan murid. Body size and build of the new rat, along with some cranial features, are similar to the Thai Leopoldamys neilli, but other cranial traits coupled with molar occlusal patterns resemble morphology in species of the Indomalayan Niviventer, Chiromyscus, and Saxatilomys. The new species is petricolous, includes insects in its diet, and was found only in talus composed of large limestone blocks. Its distribution in the reserve is likely patchy. Whether this limestone rat is restricted to the extensive karst regions of northeastern Vietnam or also occurs in southern China and elsewhere in the northern karst landscapes of Indochina, and Vietnam in particular, will be known only by conducting surveys in limestone regions outside of northeastern Vietnam.