This study investigates the core competencies required of Korean secondary-school English teachers and how they perceive these competencies in terms of importance, applicability, and teachers’ competency level ahead of implementing the 2015 revised national English curriculum in secondary schools. After the literature research, interviews, and expert review processes, five core competencies were extracted: curriculum and content reorganization competency; learner-centered teaching competency; innovative assessment competency; multicultural (intercultural) education competency; and information literacy and ICT use. From the results of a survey administered to 93 secondary school English teachers, it was found that the perceived competency level was lower than required, but it was higher than applicability. Overall, teachers felt insecure about how to apply the required competencies to their lessons. There was also a difference between middle school teachers and high school teachers in the self-rating results. These results provide implications for teacher preparation and the direction of teacher education toward the successful implementation of the 2015 revised curriculum.