In this article the historian from Japan (Tokyo) and the scholar from the Russian Federation (St. Petersburg) examined the professional activity of the several Russian naval officers (naval attaches) in Japan since the end of the XIXth century to the beginning of the Russian-Japanese War (1904-1905). The authors of the article determined the principal directions, methods and objects of the Russian attaches` activity. The scholars appreciated the value of detailed information about the strength of the Japanese Navy and military intensions and plans of the government and high command in this country. Then scholars determined and appreciated the final results of Russian naval officers` professional efforts on the eve of the war between two powerful states - the Russian and Japanese empires.