The purpose of this study was to explore teachers’ experiences in implementing the competency-based curriculum in South Korea. The following research questions were addressed: (a) What do teachers think about the changes to competency-based curriculum? (b) What kinds of learning experiences have teachers had regarding professional development? (c) What efforts have teachers made to improve their classroom teaching and assessment? (d) How do teachers perceive the learning environment in their schools implementing the competency-based curriculum? The responses of 6,299 elementary and secondary school teachers to a questionnaire survey were analyzed. The findings revealed that teachers perceived the competency-based curriculum to be important for future-oriented education, and they showed great interest in applying the curriculum. Teaching and assessment demonstrated considerable changes, including a greater emphasis on self-directed and cooperative learning as well as process-oriented assessment. To better familiarize themselves with these changes, about one half of surveyed teachers participated in in-service training programs. The school environment also changed, encouraging teachers’ cooperation and involvement in the learning community. This study discussed several challenges faced by South Korean teachers in implementing competency-based curriculum and provides recommendations for improving the curriculum to facilitate better educational reform.