This experiment was conducted to investigate the effects of yeast β-glucan and bacitracin zinc on growth performance and gastrointestinal development of early-weaned calves. Twenty healthy Holstein male neonatal calves were randomly allotted to 4 groups with 5 replicates per group and 1 calf per replicate. The control group (group A) was fed with a basal diet, groups B and C were fed with the basal diet supplemented with 75 mg/kg yeast β-glucan, and group D was fed with the basal diet supplemented with 60 mg/kg bacitracin zinc. The experiment lasted for 28 days. Feed intake (FI) was recorded every day, body weight was measured every two weeks and average daily gain (ADG) was calculated every two weeks. On day 21, the calves of groups A, B and D were challenged orally with Escherichia coli culture medium (O141∶K99), while group C was fed normally. The rectal content was collected after the challenge and diluted for microorganism counts. On day 28, calves were slaughtered and tissues from saccus cranialis, duodenum, jejunum and ileum were obtained and used in tissue slice. The results showed as follows: 1) compared with group A, the ADG of calves in group B was increased by 26.17% and 24.93% in the two phases before the Escherichia coli challenge (P<0.05), and the ADG of calves in groups B and D were increased by 30.38% and 30.81% after the Escherichia coli challenge (P<0.05); the F/G in groups B and D were significantly lower than that in group A (P<0.05). 2) Compared with group A, the amounts of Escherichia coli in rectum at 12 h and 24 h in groups B and D were significantly decreased (P<0.05), the amount of Lactobacillus in rectum in group D was significantly decreased (P<0.05), and the amount of Lactobacillus in rectum in group C was significantly higher than that in group A. 3) Compared with group A, the rumen papilla height and width of groups B and D were significantly increased (P<0.05). The crypt depth of duodenum in groups C and D were significantly lower than that in groups A and D (P<0.05). The villus height/crypt depth (V/C) in groups B, C and D were higher than that in group A (P<0.05). In conclusion, yeast β-glucan at the dosage of 75 mg/kg can ease the decrease of growth performance of early-weaned calves, improve the gastrointestinal development, and protect early-weaned calves challenged with Escherichia coli, indicating that the use of β-glucan in calves feed may decrease the usage of antibiotics.  ［Chinese Journal of Animal Nutrition， 2011， 23（5）：813 -820］