This paper examines the expansion of rice cultivation in northwestern Korea during the interwar period and its role in supplying food to Japan. The Policy to Increase Rice Production (PIRP) implemented by the Governor-General of Korea (GGK) had a significant impact in addressing food shortages and unstable rice prices in the Japanese market. As Korean rice production increased significantly, the northern regions experienced rapid growth in both paddy cultivation area and production yields, thus surpassing the traditionally dominant southern provinces. The introduction and expansion of irrigation and Japanese rice breeds propelled the transformation of land productivity, particularly in Hwanghae province. High-yield rice varieties, such as Rikuu No. 132 and Fukubōzu, further boosted production, allowing northwestern Korea to become a significant rice supplier. The expansion of sea routes complemented increased production by facilitating Korean rice exports to Japan, particularly to Osaka and Tokyo. However, Korean rice faced increasing competition from Taiwanese Hōrai rice, which had lower production costs and thus gained popularity among Tokyo customers. By the mid-1930s, Taiwanese rice exports to Japan outpaced Korean rice, again altering the dynamics of the colonial rice trade and the metropolitan economy.