This study uses document, observation, and interview to analyze ten Taiwanese elementary school English teachers' practice and exercise of leadership among other colleagues during professional dialogue and to examine what influenced the practice of leadership. This study has the following major findings. First, participants' leadership was mainly centered on improving colleagues' teaching and learning practices, rather than traditional leadership in terms of power and authority. Secondly, lack of time, negotiating with administrators, consensus among teachers, and expertise in English instruction affected participants' effectiveness in leading the meetings and discussions. Suggestions on effectively exercise leadership in professional dialogue are provided.