A 20 kDa heat-labile toxin (BFT) produced by enterotoxigenic Bacteroides fragilis (B. fragilis) is associated with diarrhea and mucosal inflammation. Although intestinal epithelial cells are known to activate mitogen-activated protein kinase (MAPK) in response to bacterial infection, there has been little understanding on the association between MAPK activation and BFT-induced enteritis. This study was performed to investigate the role of MAPK in enteritis induced by BFT. In human colon epithelial cells, BFT increased IL-8 secretion in a dose-dependent manner. BFT activated the three main MAPK cascades, including extracellular signal-regulated kinase (ERK), p38, and c-Jun NH2-terminal kinase (JNK). BFT stimulation also activated AP-1 activated signals. Overexpression of dominant-negative of the c-Jun decreased the activated AP-1 signals and the up-regulated IL-8 expression induced by BFT stimulation. In addition, SB203580 and ERK inhibitor U0126 significantly reduced IL-8 secretion in colon epithelial cells stimulated with BFT. Furthermore, SB203580 significantly prevented BFT-induced severity of enteritis and fluid secretion in mouse ileum. These results suggest that MAPK activation may be required for IL-8 transcription in intestinal epithelial cells exposed to BFT and that the activated MAPK can mediate intestinal inflammation and mucosal damage induced by BFT.