Roman Dmowski’s journey to Japan after the outbreak of the Russo-Japanese War is a well-known episode in the modern history of Poland. As far as we know, Dmowski, after his arrival in Japan, wrote two memorandum in English (one is about political and social relations in Russia and the another is about the political situation in Poland) for the Japanese General Staff, and in the name of the Japanese government wrote an appeal to Polish soldiers in the Russian army to leave it and surrender. In a street in Tokyo Dmowski by chance met Józef Piłsudski, a member of the Polish Socialist Party and Dmowski’s political opponent, who was also visiting Japan, seeking for military aid from the Japanese government. Three days later they had their famous „nineteen hours’ talk” at the hotel. After it Dmowski sent a memorandum to Baron Jutarō Komura, Japanese Minister of Foreign Affairs, in which he expounded how harmful it would be for the war strategy of Japan if an insurrection breaks out in Poland. Besides these activities, we should pay due attention to the effect of Dmowski’s stay in Japan on his view of nation or society. Dmowski’s nine weeks stay in Japan (from 15 May to 22 July, 1904) was only in a part of the first stage of the war which broke out in February 1904 and ended in June 1905. Despite this fact, it should be emphasized that Dmowski’s knowledge about Japanese people was so much richer than we suppose. This paper presents some interesting episodes with a special Focus on the conversation with General Gentarō Kodama and his experience of his visits to Japanese prisoner-of-war camps in Matsuyama, where he interviewed Polish soldiers. Dmowski was strongly impressed by the behavior and way of thinking of Japanese people and stated later that it influenced his views immensely, among others his view on society and the nation. The effect of his experience in Japan mostly ap pears in his work „Essentials of Polish Politics” which was published in „The All- Polish Review” in May 1905 and was added as supplementary chapters to the third edition of „Thoughts of a Modern Pole” (1907). In this important article the father of modern Polish nationalism could clarify his views on „national instinct” and „national ethics”.