This experiment was conducted to investigate the effects of yeast β-glucan on organ development, gastrointestinal morphological development and quantity of microflora in rectum of early-weaning calves. Forty-two neonatal healthy Holstein calves were randomly allotted to 6 groups with 7 replicates each and 1 calve in each replicate. All calves were fed with diets supplemented with 0 (control group), 25, 50, 75, 100 and 200 mg/kg yeast β-glucan, respectively. The experiment lasted for 56 days. On day 56, calves were slaughtered, tissues from saccus cranialis, duodenum, jejunum and ileum were obtained and used in tissue slice, and the rectal content were collected and diluted for microorganism counts. The results showed that β-glucan might promote rumen-reticulum growth, however, the differences were not significantly (P>0.05); compared with other groups, the ratio of villous height to crypt depth was significantly higher in calves fed diet supplemented with 75 mg/kg β-glucan (P<0.05); when β-glucan supplemented at 75 mg/kg in diet, the number of Escherichia coli in rectum was significantly decreased compared with the control group (P<0.05), and the number of Lactobacillus was significantly higher than other groups (P<0.05). It was concluded that supplementation of 75 mg/kg β-glucan could increase the height of intestinal villi, the ratio of villous height to crypt depth and adjust the structure of intestinal microflora, thus decreased the incidence of disease and had a health-promoting effect on the growth of claves.［Chinese Journal of Animal Nutrition, 2009，21(6）:846-852］