This study is designed to clarify the changes of composition and enzyme activities of the small intestinal mucosa in fasted rats. Starvation for 3 days caused marked decreases in body weight, DNA and protein of small intestinal mucosa, and the activities of digestive enzymes. After starvation for 3 days, rats were refed with the laboratory chow for 1, 3 and 7 days. 1) The body weight of rats recovered in 3 days. 2) The recovery of the small intestinal mucosa was very rapid, especially its dry weight and DNA. 3) Both sucrase and alkaline phosphatase activities increased markedly, then returned to the control level in 7 days.