This study is to prove out that Japan seized Dokdo forcedly by its strategic value at the Battle of East Sea during the Russo-Japanese War. Additionally, this study aims at asking some researchers to reconsider who take no account of the fact that Japan’s forced seizure of Dokdo was committed as a step toward complete colonization of Korea. That is to say, Japan’s forced seizure of Dokdo was just not an incident to capture an island but Japan’s intentional forced seizure for the victory at the Battle of East Sea and further at the Russo-Japanese War. Actually, Japan won the Russo-Japanese War, and then Japan was able to colonize Korea completely and successfully. Above all, it is pointed out that Japan’s justification for the forced seizure of Dokdo, that is, Japan’s insistence on the acceptance of Nakai Yosaburo’s petition to incorporate Dokdo into Japan’s territory is just a fiction. He already knew that Dokdo was an annexed island to Ullengdo of Korea. For his fishing business, he planned to ask for a lease from the Korean government via the Ministry of Trade and Commerce of Japan. However, it is found out that he submitted the petition abetted by officers, who fronted for Japanese overseas invasion, like Maki Naomasa(Director of the Fisheries Bureau of the Ministry of Agriculture and Commerce), Kimotsuki Kaneyuki(Hydrographic Director of Japanese Navy), Yamaza Enzaburo(Director of Governmental Affairs of the Ministry of Foreign Affairs). The submission of the petition abetted by these officers tells us that Japanese government power intervened in the forced seizure of Dokdo. To inquire into why the national power as mentioned above intervened into that matter, the battle situations of the Vladivostok Fleet in the East Sea are examined out. The Fleet was defeated in the battle in the coastal waters of Ulsan. But previously, it damaged much the Japanese combined fleets. And hearing about the organization of the Baltic Fleet(the Second Pacific Squadron), Japan had to give the Battle of East Sea first thought. As a result, Japan government made Nakai Yosaburo submit the petition on the incorporation of Dokdo. The procedure of incorporating Dokdo led to the forced seizure of Dokdo by Japan. This study tries to clear out that the forced seizure of Dokdo is an indispensable step or measure of Japan for the victory of the Battle of East Sea. However, this writer admits frankly that the related evidences for that matter end up in circumstantial ones. However, under the circumstances that Japan refuses to go public with the related materials on the ground of the judgement of Japan’s Supreme Court that it is righteous not to go public with the disadvantageous materials to Japan government, it should be added that it is not easy to prove a logical inconsistency of the Japanese unilateral declaration for Dokdo. (Yeungnam University/wkkim@ynu.ac.kr)