Changes in environmental temperature affect the morphology and function of digestive tract in wild rodents. The small intestine is the main absorptive organ for nutrients, and its structure and function are plastic. To understand the response mechanisms of the structure and function of small intestinal mucosa to environmental temperature, we investigated the effects of cold acclimation on small intestinal mucosal structure and mucosal immunity-associated cells in Brandt's voles (Lasiopodomys brandtii). We found that: 1) The villus length and the ratio of villus length to crypt depth (V/C) in the cold group were higher than that in the control group. 2) Cold acclimation increased the number of endothelial lymphocytes in the small intestine. 3) Cold acclimation significantly increased the number of goblet cells in the duodenum, the jejunum and the ileum. These results indicate that  the structure of small intestinal mucosa and the number and distribution of immune cells may undergo plastic changes in cold environments. These changes may be related to high energy demand and changes of immune function .