Thorold's deer is one of the largest deer species, with a shoulder height around . Males, which typically weigh from , are significantly larger than females, at in weight. The hair is coarse and grey-brown over most of the body, fading to yellowish buff on the underparts, with a distinct reddish-brown patch on the rump, and a ridge of darker hair running down the spine. During winter, the coat is paler, and about twice as thick as during the summer, being thicker even that of a moose. The head is darker than the rest of the body, especially in males, and contrasts with pure white markings on the lips, around the nose, and the throat just below the chin.