The purpose of this study is to explore the perceptions of 10 experienced junior-high science teachers concerning their learning experiences with inquiry teaching, and the perceptions of their own professional development. An ITEQ questionnaire and semi-structured interview were used for data collection and a grounded theory method used for analysis. The findings indicate that there are two dimensions of the process of inquiry teaching professional development, including epistemology and teaching practice transformation. These case teachers changed their epistemology from positivism to constructivism based on their previous learning experience and their experience of the course. After the case teachers changed their epistemology, they increased their flexibility in designing inquiry lesson plans and in their inquiry teaching repertoire. While implementing inquiry lessons, these teachers still faced a dilemma concerning student learning outcomes vs. pressures from school, but their teaching beliefs, reflections and support systems were critical factors reinforcing their persistence in implementing inquiry teaching.