Heat of swelling of the eight kinds of seaweed Arame (Eisenia bicyclis), Hiziki (Hizika fusiformis), Asakusanori (Porphyra tenera), Tengusa (Gelidium amansii), Wakame (Undaria pinnatifida), Aonori (Enderomorpha profifera), Mafunori (Gloiopelfis tenax) and Kombu (Laminaria japonica), which are used for food in Japan, were measured. The swelling of seven types was exothermic. However, that of Kombu was endothermic. The dependence between water content and the heat of swelling of Kombu showed a concave upward curve, with a minimum value at approximate to 0.1gg(-1) of water content. The dissolution of Kombu extracts was endothermic and the swelling of "Kombu ghost" (Kombu grounds) was exothermic. From the dependence on the water content of the heats of the dissolution of the Kombu extracts and the swelling of the Kombu ghost, we conclude that the endothermic phenomenon for the swelling of Kombu is derived from the sum of the heats of dissolution of water-soluble components in Kombu and the heat hydration of the insoluble skeleton.