This article examines the Siberian Diary of Enomoto Takeaki, an essential figure in the 19th-century Japanese diplomacy, as a source for understanding Siberia’s socio-economic landscape and the evolution of Russian-Japanese relations. Following his successful negotiation of the 1875 Treaty of St. Petersburg which resolved territorial dispute between Russia and Japan by exchanging Sakhalin for the Kuril Islands, Enomoto embarked on an overland journey from Tsarskoye Selo (near St. Petersburg) to Vladivostok in July – September of 1878. During this trip, he kept travel records named the Siberian Diary, which provides an eyewitness perspective on a region rarely documented by Japanese observers. The diary contains details on several key areas. Among them, there are economic activities (gold mining technologies and production); social observations, such as ethnic composition of Russia population (for instance, Tatars and Buryats) and the penal exile system. The diary also analyzes political and military structures, assessing garrison strengths and noting the situation along the Russian-Chinese border. The Siberian Diary combines the traditional Japanese literary genre of travel writing with practical intelligence-gathering objectives. Enomoto intended both to identify potential technological innovations for Japan’s development and to familiarize Japanese readers with Russian society. The diary was first published in 1934 and until this day was not translated into foreign languages, resulting in its limited examination within academic literature. The document represents a pioneering achievement in the direct Japanese engagement with Russia. It can be used as a resource for scholars of the Siberian history and cross-cultural perception.