This type of weasel is named for its yellow-colored underbelly; the upperside of the body and the tail are of a dark brown. Yellow-bellied weasels can grow up to 9.8–10.6 inches (25–27 cm) long. The tail is 4.9–5.9 inches (12–15 cm) long. It weighs about 3.3 pounds (1.5 kg).