The article focuses on the Russian minister to Japan R. R. Rosen’s role at the negotiations that preceded the war of 1904 – 1905. Because of quite long stay at the diplomatic service in Japan, he could study Japanese interests in East Asia and the attitude of the Japanese society to the Russian Empire claims to the control over Manchuria and Korea thoroughly. Being informed about military potential of Japan, R. R. Rosen stated that rise of armed conflict was extremely undesirable; however, in spite of his efforts, Saint-Petersburg and Tokyo couldn’t strike a happy medium.