This study reports teachers' learning through action research on students' conceptual understanding. The study examined (a) the teachers' views about science teaching and learning, (b) the teachers' learning about their teaching practices and (c) the conditions that supported the teachers' learning through action research. A total of 14 elementary in-service teachers' course discussion, self-video reflection, action research reports, and learning reflection were analyzed. Findings revealed that (a) the teachers in this study commonly espoused the importance of probing and utilizing students' preconceptions in science teaching, but they demonstrated various levels of epistemological understanding of student learning and teaching, (b) the teachers experienced the action research as a means to evaluate science teaching methods and changing their teaching practices, and (c) the teachers identified sharing goals, problems, and solutions as an essential supporting condition for their learning through action research. Implications for professional development and further research are discussed.