The objective of this study was to evaluate the effects of repeated oral exposure to LPS on humoral immune responses of periparturient dairy cows. Sixteen Holstein cows were assigned to two treatment groups 2 wk before the expected day of parturition. Cows were administered orally, twice weekly at wk -2, -1 and +1 around parturition, with the following treatments: 3 ml saline; or 3 ml of saline containing LPS from Escherichia coli 0111:B4. The amount of LPS administered during wk -2, -1, and +1 was 0.01, 0.05, or 0.1 µg/kg body weight, respectively. Multiple blood samples were collected by jugular vein and various immune and clinical variables were measured. Results indicated that, on one hand, concentrations of plasma IgG anti-LPS Abs decreased (P < 0.01) and those of IgM anti-LPS Abs increased (P < 0.01) in cows treated with oral LPS. On the other hand, there were no overall differences (P > 0.05) in the concentrations of serum amyloid A, LPS-binding protein, haptoglobin, cortisol, IgA anti-LPS Abs in the plasma, feed intake, body temperature and rumen contractions rate between the control and treatment groups. To our knowledge, this study is the first to show that repeated oral administration with LPS from E. coli 0111:B4 has the potential to stimulate humoral immune responses in periparturient dairy cows.