The paper features some aspects of Chinese colonization policy in the Mongolian North in the early XX century. There have been publications on the issue; however, they fail to provide a full coverage of the period, and no serious comprehensive study has ever been performed. In this regard, documents of the State Archive of the Russian Federation can contribute to the comprehensive study of the topic. The documents are mostly represented by trip reports to Manchuria in the first quarter of the XX century. The article describes a document about a little known event of the period in question: the trip made by the Chinese Minister of Colonies Prince Su to the territory of South-Eastern Mongolia (North-Eastern China). The author also analyzed the related conclusions made by the Actual State Councilor D. D. Pokotilov, the Extraordinary Envoy and Plenipotentiary Minister in Beijing. The paper also contains a revision of Chinese colonial policy in the Mongolian lands, made by Prince Su in his report to the Chinese authorities. The beginning of the XX century became the climax of the Chinese colonization on the territory in question. This period is also associated with the expansion of Russian influence on the territory of the Sino-Eastern railway right of way. Nevertheless, a complete picture of Chinese colonization requires further studies of archival sources.