|This study explored ways to implement a competencies-based curriculum in schools by reviewing exemplary cases that have introduced Key Competencies (KCs) in the school science curriculum. Since the OECD redefined key competencies as ``what people should know and do in order to lead a successful life in a well-functioning society``, many countries have emphasized the use of a competencies-based curriculum. Foreign and domestic classroom cases, which have used a competencies-based curriculum in science teaching, were collected and analyzed. Through open-ended interviews with teachers and principals, we investigated changes of teachers` professional knowledge and practice that were evident as a result of the implementation of competencies-based curriculum in science class. Foreign science teachers suggested ways to relate competencies-based curriculum and science curriculum including maintaining a balance between competencies-based curriculum and content-based curriculum. They also integrated KCs into all subject-based curriculums, gave priority to KCs over subject matter knowledge, and developed KCs through teaching science contents that students wanted to learn. On the other hand, Korean science teachers suggested reconstructing competencies-based curriculum by extracting common attributes from the existing subject areas. They also made KCs realized through content teaching, and developed various KCs within science contexts. Implications of the competencies-based curriculum for science teaching and learning were discussed at the end.