Many stakeholders tend to believe that native English-speaking teachers are more qualified and legitimized in teaching English only in English in the EFL context. Considering the theoretical importance of language ideology in understanding pedagogical practices, this study takes the approach that the proactive adaptations of the English-only policy into contemporary EFL classrooms are ideologically driven. Drawing on data from ethnographic fieldwork at an English-only language school in South Korea, this study examines the ways in which Korean bilingual teachers at the school interpreted, valorized, or challenged the monolingual policy in and out of classroom. While the school required Korean bilingual teachers to stick to the English-only policy, they showed different responses to the school's policy in terms of students using their first language and the expansion of the English-only policy beyond the classroom. Results suggest that the teachers' everyday practice of the English-only policy is a complex process of negotiating interconnected ideologies and identities related to native-speakerism, gendered nationalism, and professionalism. The academic need for the local and ethnographic understanding of the language policy and its professional implications for nonnative English teachers are discussed.