Immigrants to South Korea are a diverse group that includes marriage immigrants, migrant workers, Koreans with foreign citizenship and refugees. Due to this, the policy on immigrants has evolved from earlier forms focusing on regulating immigration based on discrimination and exclusion, to integration and assimilation policies supporting multiculturalism. There are previous studies on immigrant policies and literature reviews both at home and abroad, but the factors that impact on policy diffusion have not been fully analyzed in Korea. This study reviews multicultural family support policies adopted by 153 local governments from 2007 to November 2012, and analyzes the impact of internal determinants which include financial and economic factors, consisting of self-generated revenue, per capita self-generated income, percentage of social welfare budget and urbanization, social and cultural factors including percentage of foreign population, the number of marriage immigrants and their children and the number of civil society organizations, and political and administrative factors including the political orientation of heads of local governments and city council members, election time and acceptance of policies for foreigners. The results suggest that variables of regional diffusion, per capita self-generated income, spending on social welfare, and the acceptance level of policies for foreigners are most significant, while the numbers of marriage immigrants and their children, the number of civil society organizations, and the heads of governments of local governments political orientation are partially significant.