Abstract: Diarrhea is a common disease of weaned piglets which poses a great threat to the development of pig industry. The prevention and treatment experiments were conducted to evaluate the clinical effect of a commercial peptide additive Baibeitai on diarrhea of 4-week-old weaned piglets. In prevention experiment, the prevention rate of group Ⅰ, group Ⅱ, group Ⅲ （Baibeitai peptide additive） and group Ⅳ （antimicrobial agents） were 95.0%, 97.5%, 92.5% and 88.5%, respectively. In treatment experiment, the cure rate of group Ⅰ, group Ⅱ, group Ⅲ （Baibeitai peptide additive） and group Ⅳ （antimicrobial agents） were 91.7%, 86.6%, 81.2% and 76.5%. The clinical effect of Baibeitai peptide additive on weaned piglets diarrhea was proved to be superior to that of antimicrobial agents, and the peptide additive had a positive influence on feed intake and ratio of feed to gain of weaned piglet.