Abstract: The age at which starter is supplied to lambs can affect the development of the intestinal tract. To determine the effect of the age of starter supply on the morphology of the rumen and small intestine of lambs, 72 healthy male Hu lambs (two lambs per litter, birth weight 3.51±0.52 kg) were randomly divided into two groups: one group was supplied with starter at 7 days after birth and the other at 42 days after birth. Six lambs were selected at random for slaughter on day 14, 28, 42, 56, 70, and 84, respectively. The results showed that the rumen papillae in the dorsal sac and the ventral sac were significantly longer in the 7-day group than in the 42-day group at 42 days (P<0.05). Also, the rumen papillae in the ventral sac tended to be wider in the 7-day group than in the 42-day group at 42 days (P=0.053). The rumen muscle layer in the dorsal sac was thicker in the 7-day group than in the 42-day group at 42 days (P<0.05). The villus length, and the ratio of villus length to crypt depth of the duodenum and ileum were significantly greater in the 7-day group than in the 42-day group at 42 days (P<0.05). The depth of the ileum crypt was smaller in the 7-day group than in the 42-day group at 42 days (P<0.05). Together, these results show that supplying starter from 7 days of age could improve the development of the rumen epithelium before 84 days and the small intestinal mucosa before 42 days.