To determine whether alpha-linked galacto-oligosaccharide (alpha-GOS) prevents allergic peritonitis, BALB/c mice were fed a synthetic diet with and without alpha-GOS supplementation for 7 d, and were then subcutaneously immunized with ovalbumin on days 0 and 7. The mice were challenged by intraperitoneal injection with ovalbumin on day 14, followed by peritoneal lavage on day 15. The total number of peritoneal exudate cells was significantly lower in the mice fed the alpha-GOS diet than in those fed the control diet. Peritoneal lavage fluid from mice fed the alpha-GOS diet not only had less potency to attract peripheral blood leukocytes and peritoneal exudate cells ex vivo, but also had lower concentrations of monocyte chemoattractant protein-1 (MCP-1) and eotaxin. Preincubation of the cells with alpha-GOS failed to affect the migration to peritoneal lavage fluid. We propose that dietary alpha-GOS reduces cell infiltration in allergic peritonitis by reducing antigen-induced elicitation of MCP-1 and eotaxin in mice.