We previously reported that consumption of glucomannan-containing food (lily bulb) modulates gut microbiota and increases gut immunoglobulin A (IgA, index of intestinal immune function), mucins (index of intestinal barrier function), and colonic alkaline phosphatase (ALP) activity in rats fed a high-fat (HF) diet. Small intestinal ALP has an established protective effect in inflammatory diseases, whereas little is known about the function of colonic ALP activity. We hypothesized that dietary glucomannan would increase colonic ALP activity and the gene expression in rats fed an HF diet. To test this hypothesis, male Sprague-Dawley rats were fed a diet containing 30% lard with or without 4% high or low viscous glucomannan (HGM or LGM) for 2 weeks. Dietary HGM and LGM significantly increased colonic ALP activity without affecting ALP activity in the small intestine. The colonic expression of IAP-I, an ALP gene expressed throughout the intestine, was significantly higher in the HGM and LGM groups when compared with the control group. The colonic expression of Akp3 and Alpl, other ALP genes, were not affected by HGM and LGM. Dietary HGM and LGM significantly elevated fecal levels of IgA and mucins and cecal organic acids, including n-butyrate, propionate, and lactate. Colon ALP correlated with fecal IgA, mucins, and cecal organic acids. The present study showed that dietary glucomannan elevates colonic ALP activity by up-regulation of the expression of IAP-I, which might be important for protection of gut epithelial homeostasis.