Many studies have shown that esterified phosphorus (P) in diets has a favorable effect on mineral absorption in humans and animals. Phosphorylated oligosaccharides derived from potato starch increase calcium (Ca) absorption from the rat intestine both in situ and in vitro. We hypothesized that the feeding of potato starch has a potential to increase Ca or magnesium (Mg) absorption. Male Sprague-Dawley rats at 7 weeks were fed 4 types of diet containing either 60% sucrose, cornstarch, or 1 of 2 types of potato starch with different P contents for 1, 3, or 5 weeks. A balance test for Ca, Mg, and P was undertaken, and these mineral contents in the femur were determined for the 4 diet groups at each feeding period in vivo. Ingestion of potato starch increased Ca, Mg, and P excretion into feces and decreased the absorption rate of Ca and Mg. Femoral Ca contents were also decreased in the rats fed the potato starch diets compared with those in rats fed the sucrose or cornstarch diet. In vitro experiment in Ca absorption was undertaken using everted jejunal and ileal sacs of the small intestine in male Sprague-Dawley rats (7 weeks old). The potato starch application did not induce significant increase in Ca absorption compared with nonstarch (control) or cornstarch application. In conclusion, the ingestion of potato starch does not increase Ca and Mg absorption and rather accelerates their excretion, inducing the decrease in mineral absorption and retention in growing rats.