In recent years lithium has been used increasingly as a second battery, particularly in the field of electric information device, because of its high energy density and output voltage. However, we import the necessary amount of lithium from foreign countries since there is no available lithium mine in Japan. In order to secure constantly a sufficient amount of lithium in Japan, special attention has been paid to lithium ion dissolved in Seawater. A recent estimation indicated that at least 200 billion tons of the lithium ion are dissolved in the whole seawater. We propose a floating system to extract lithium from seawater using such ocean energies as sea wave and sea current. For three years from 2000 to 2002, we performed several investigations to develop techniques for practical use of the floating system. In this paper, we report the results of our investigations, as the first step toward the practical use.