CCL28 induces the migration of IgA Ab-secreting cells (ASCs) via CCR10 and also displays a potent antimicrobial activity in vitro. To explore the role of CCL28 in vivo, we generated CCL28-deficient mice. The mice exhibited a significant reduction and abnormal distribution of IgA ASCs in the lamina propria of the colon. The concentrations of total and Ag-specific IgA in the fecal extracts of CCL28-deficient mice were also drastically reduced. The average amount of IgA secreted by a single IgA ASC derived from the colon was also substantially reduced in CCL28-deficient mice. Furthermore, CCL28 was found to significantly increase the average amount of IgA secreted by a single IgA ASC derived from the colon in vitro. In contrast, the generation of IgA ASCs in Peyer's and cecal patches was not significantly impaired in CCL28-deficient mice. We also found a relative increase in the Class Bacilli in the fecal extracts of CCL28-deficient mice and demonstrated a potent antimicrobial activity of CCL28 against Bacillus cereus and Enterococcus faecalis, both of which belong to Class Bacilli. Thus, CCL28 may also suppress the outgrowth of some bacterial species by its direct antimicrobial activity. Finally, CCL28-deficient mice exhibited a highly aggravated dextran sodium sulfate-induced colitis that was ameliorated by pretreatment with antibiotics. Collectively, CCL28 plays a pivotal role in the homing, distribution, and function of IgA ASCs in the colon and may also affect the intestinal microbiota through its direct antimicrobial activity.