An experiment was designed to evaluate the bioavailabili-ty of purple layer (Asakusa-Nori, Porphyra tenera Kjellman) magne-sium (Mg) in Mg-scarcity Fischer 344 male rats from serum Mg level, kidney calcification and bone Mg contents. Male rats of 4 weeks of age were divided into four groups of six rats. The four groups were con-trol (20SC), Mg-restricted (-Mg20SC), -Mg20SC plus purple layer (-Mg20SCP), and 20SC plus purple layer (20SCP) group respectively. To-Mg20SC, 1/10 Mg of the 20SC diet was added.-Mg20SCP diet was prepared to contain equal amount of Mg as in the 20SC diet with purple layer as a Mg source. 20SCP diet was designed to contain double amount of Mg. After a 3-week experimental period, rats were decapi-tated. Blood serum, right kidney, and right femur were collected and Mg, calcium (Ca), phosphorus (P) were determined. Serum Mg concentra-tion of the-Mg20SC was 1/3 of the 20SC, indicating apparent hypomag-nesemia. Serum P also showed lowered concentration. On the other hand, the serum Ca indicated higher value than the other groups, indicat-ing hypercalcemia. Addition of purple layer to-Mg20SC diet resulted in a normal serum Mg, Ca, and P level. The Mg-scarcity (-Mg20SC) rats accumulated much amount of kidney Ca. Whereas, there was no signifi-cant difference in kidney Ca between control (20SC) group and purple layer-supplemented (-Mg20SCP) rat group. The-Mg20SC rats showed lowered ash content and reduced Mg and P concentrations in the femur. Purple layer supplementation increased the ash, Mg, and P. All of the results indicated that the purple layer Mg was used as a Mg source.