Attitudes toward immigrants and immigration policies are divisive issues in American politics. These attitudes are influenced by factors such as political orientation and religiousness, with religious and conservative individuals demonstrating higher prejudice toward immigrants and refugees, and endorsing stricter immigration policies. Christian nationalism, an ideology marked by the belief that America is a Christian nation, may help explain how religious nationalist identity influences negative attitudes toward immigrants. The current research addresses this through four studies among participants in the US. Across studies, our results showed that Christian nationalism was a significant and consistent predictor of anti-immigrant stereotypes, prejudice, dehumanization, and support for anti-immigrant policies. These effects were robust to inclusion of other sources of anti-immigrant attitudes, including religious fundamentalism, nationalism, and political ideology. Further, perceived threats from immigrants mediated the relationship between Christian nationalism and dehumanization of immigrants, and attitudes toward immigration policies. These findings have implications for our understanding of the relations between religious nationalism and attitudes toward immigrants and immigration policy in the US, as well as in other contexts.