In conclusion, the data generated by this study demonstrated that a diet supplemented with 300 mg/kg COS or 50 mg/kg chlortetracycline in weaned piglets decreased feed conversion ratio, the villus width, the crypt depth and TLR4mRNA expressions, but increased villus length, villus length/crypt depth and GCs. There was no observed effect on Claudin-1 mRNA expression. Furthermore, COS had a better effect on IELs than chlortetracycline, and COS showed positive activity but chlortetracycline caused a negative effect on occludin and no significant effect on sIgA protein expression. This illustrates that COS and the antibiotic have similar effects on promoting animal growth and reducing intestinal inflammation, but have different effects on animal intestinal mucosal barrier function. To sum up, this study shows that chitosan has the potential to replace chlortetracycline as a feed additive for pigs.