This study examines South Korean secondary social studies teachers' conceptualizations of multiculturalism and how they interact with ethnic nationalism based on the concept of a pure bloodline, Korean identity and teaching practices in an emerging multicultural society. Throughout several revisions of the national standards curriculum responding to the changing society, multiculturalism has become a dominant discourse in education and has influenced the social studies curriculum for more than a decade. Middle and high school social studies teachers started to see more "Damunhwa" (multicultural) students along with the curriculum changes. Utilizing a qualitative method, especially critical discourse analysis (CDA), I investigated how secondary social studies teachers understood multiculturalism in their professional and personal lives. Further, I analyzed how these understandings influenced ethnic nationalism based on the concept of a pure bloodline that has been internalized as a criterion of Korean identity. Finally, I analyzed how these conceptualizations of multiculturalism, ethnic nationalism, and Korean identity interacted with teachers' teaching practices. I conducted interviews with 20 social studies teachers in one metropolitan city of South Korea. The results indicate that secondary social studies teachers are knowledgeable about the new curriculum content while they have little understanding of "Damunhwa" students due to a systemic obstacle and "Damunhwa" students' reluctance of revealing their backgrounds. Moreover, teachers experience the discrepancy between what to teach and how they feel with regard to people from diverse backgrounds due to their prejudice and bias that have been constructed in Korean society. Also, teachers show the multiple layers of the constructed meaning of "Damunhwa" such as separation, negativity and charity connotation. While they strongly oppose ethnic nationalism, teachers rarely demonstrate an alternative idea of what it means to be Korean in a multicultural society. Based on the interview analysis, several imperatives in secondary social studies education emerge to prepare for a better teaching practice in a multicultural society. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]