A total of 50 weaning pigs (16 d of age; 4.72 +/- 0.23 kg of BW) were selected to investigate the effect of dietary chito-oligosaccharide (COS) supplementation on growth performance, fecal shedding of Escherichia coli and Lactobacillus, apparent digestibility, and small intestinal morphology. Pigs housed in individual metabolic cages were assigned randomly to 5 treatments (n = 10), including 1 basal diet (control), 3 diets with COS supplementation (100, 200, and 400 mg/kg), and 1 diet with chlortetracycline (CTC) supplementation (80 mg/kg). Fresh fecal samples were collected to evaluate shedding of E. coli and Lactobacillus on d 0, 7, 14, and 21 postweaning. Fresh fecal samples collected from each cage from d 19 to 21 were stored frozen for determination of apparent total tract digestibility. On d 21, all pigs were killed to collect the middle sections of the duodenum, jejunum, and ileum for determination of mucosa morphology. Supplementation of COS at 100 and 200 mg/kg and supplementation of CTC improved (P < 0.05) overall ADG, ADFI, and G:F in comparison with the control. Supplementation of COS at 200 mg/kg as well as supplementation of CTC increased (P < 0.05) apparent total tract digestibility of DM, GE, CP, crude fat, Ca, and P, whereas COS at 100 mg/kg increased (P < 0.05) the digestibility of DM, Ca, and P in comparison with the control diet. Pigs receiving diets supplemented with COS or CTC had a decreased (P < 0.05) incidence of diarrhea and decreased diarrhea scores compared with control pigs. Fecal samples from pigs receiving diets supplemented with COS had greater (P < 0.05) Lactobacillus counts than those from control pigs and pigs receiving diets supplemented with CTC on d 14 and 21. However, supplementation of COS at 200 mg/kg and supplementation of CTC decreased (P < 0.05) E. coli counts in the feces on d 21 compared with the control diet. Dietary supplementation of COS at 200 mg/kg and of CTC increased (P < 0.05) the villus height and villus:crypt ratio at the ileum and jejunum, and COS at 100 mg/kg also increased (P < 0.05) the villus height in the ileum compared with the control diet. The current results indicated that dietary supplementation of COS at 100 and 200 mg/kg enhanced growth performance by increasing apparent digestibility, decreasing the incidence of diarrhea, and improving small intestinal morphology.