Head and body length is 16–17 cm. Tail is 20–22 cm. Grayish brown with a reddish tinge dorsally, darkest along back. Underparts gray grading into whitish. Chin and upper throat white. Tail blackish brown with fine dark hairs. Long, shiny black whiskers. Fur soft and long, up to 45mm in length in back. Feet covered with short hairs.
The Nillu rat is only found in Knuckles, Horton Plains, Nuwara Eliya, and Ohiya in the central highlands of Central and Uva provinces of Sri Lanka.