This study explores how informal inquiry among teachers occurs in pursuit of their professional development within a learning community that has been voluntarily constructed by South Korean teachers. To this end, the study investigates what leads teachers to participate in a self-organized learning community, how informal inquiry occurs in the community, and what this informal inquiry means for teachers in the community. The findings show that learning communities self-organized by teachers have the force to maintain and develop themselves without any external rewards or support because of the similar status and work experience of the teachers and the resulting parity in their relationships. The findings also demonstrate that through informal inquiry, some teachers have not only increased their knowledge of instructional practice but also transformed their attitudes toward the teaching profession. The study indicates that by providing opportunities for teachers to keep developing their professional identity and sense of autonomy, a self-organized learning community can become a place that contributes to helping teachers become "reform agents" capable of continually improving their teaching practice.