This paper intends to newly examine the formation and use of the immigration policy for Joseon farmers into Manchuria in the 1930s. For this purpose, it will put its focus on the foundation background and the business details of Seonman Colonization Co., Ltd., which was a state policy immigration company founded in 1936, and Manseon Colonization Co., Ltd., the affiliated company of Seonman Colonization. It will also pay its attention to the whole process that Manseon Colonization became unified into Manchu Colonization. In 1931 after Manchuria was built up, Joseon people’s immigration into Manchuria was characterized by permissive voluntary immigration, but it was changed into plan, control-based policy immigration with quantitative, qualitative, and regional restrictions in 1936 when Seonman Colonization Co., Ltd., which was a state policy immigration company taking full charge of Joseon farmers’ immigration into Manchuria separately from Japanese immigration, and its affiliated company, Manseon Colonization Co., Ltd., were founded. Seonman Colonization was involved in pioneering the northern part of Joseon and making investment and loaning for its affiliated company, Manseon Colonization. On the other hand, Manseon Colonization assimilated Dongah Gwonup Co., Ltd. and worked on the purchase of lands for the settlement of Joseon people, the loaning for agriculture, and the creation of independent farmers. This immigration policy for Joseon people into Manchuria, which was based on clear national discrimination, was totally corrected because the war between China and Japan, which broke out in 1937, required Joseon residents in Manchuria to cooperate during the wartime and the ideology of 5-nation cooperation had to be systematically completed. That is, Seonman Colonization became assimilated into Dongyang Colonization Co., Ltd. and then, reorganized into Bukseon Development Co., Ltd., but Manseon Colonization became unified into Manchu Colonization Corporation which took full charge of Japanese’ immigration into Manchuria. While Joseon people’s immigration into Manchuria became entrusted to Manchu Colonization, the immigration organization for Japanese, it got positioned in the same level as Japanese’ immigration. The unification of Manseon Colonization and Manchu Colonization can be regarded as the systematic completion of the 5-nation cooperation ideology which was the spirit of the national foundation of Manchuria reflecting the shock of China-Japan war in 1937. The previous researches highlighted the initiative of Gwandong Army in Joseon people’s immigration into Manchuria during Manchu period, but actually, Japanese Government-General of Joseon worked for it more actively. That is, the foundation of Seonman Colonization, which took charge of Joseon people’s immigration into Manchuria in the 1930s, was the top of ‘Ugaki Policy’, which suggests that Japanese Government-General of Joseon was the planner of the immigration policy for Joseon people into Manchuria.