Antibiotics have been widely used in piglet diets to promote growth performance and reduce diarrhea incidence. However, the resistance of pathogens to antibiotics and the possibility of residues of antibiotics in animal products induced a growing interest in the use of alternatives to in-feed antibiotics. Chitooligosaccharide (COS) is currently being tested as a substitute for in-feed antibiotics. Chito-oligosaccharide is a natural alkaline polymer of glucosamine with a number of bioactive groups (e.g., amino and hydroxyl). In weaned piglets, COS had effects on promoting growth, which may be related to its action on intestinal morphology, imune ability and microflora functions. However, previous studies showed variable results with effective doses ranging from 100 mg/kg to 5 g/kg. Thus, the present study was conducted to explore the effects of COS in low doses on intestinal morphology on swine jejunal explants. The intestinal explants were exposed for 4 h to different treatments: control, COS at equivalents concentrations to 25 mg/kg of feed (25COS) or 50 mg/kg of feed (50COS). The histological changes were evaluated using an adapted tissue score based on the intensity and severity of lesions. Dose-dependent histological lesions were observed after exposition to treatments 25COS (p=0.02) and 50COS (p=0.003) in relation to control samples. They included flattening and coalescent villi, lysis and flattening of enterocytes and oedema in the lamina propria. Villi length was a sensitive endpoint, decreasing around for 21.81% (p=0.04) and 32.75% (p=0.006), after the exposition to 25COS and 50COS, respectively. Mitotic figures were observed in the crypt epithelium and the crypth depth was maintained in all experimental groups. In accordance, the villus height:crypt depth was significantly decreased in samples exposed to 25COS and 50COS compared to control group, respectively (p≤0.01). These results indicate a toxic effect of COS in the explants model from weanling pigs after 4 h of incubation. The research will provide guidance on the low dosage of COS supplementation on weaning pigs.