Inquiry-based instruction has been promoted worldwide to achieve scientific literacy among citizens. This kind of reform-based instruction requires science teachers to have specialized knowledge called pedagogical content knowledge (PCK) for teaching science, which includes a set of knowledge and beliefs. Orientations to teaching science are considered as an overarching component, which shapes and are shaped by the other components of PCK. This mixed-methods research aims to investigate the influence of an inquiry-based professional development on 67 science teachers' pedagogical orientations. Both quantitative and qualitative data were collected before and after the professional development, using a contextualized pedagogical orientation test with multiple-choice questions and written formats. The quantitative data were analyzed using Mann-Whitney U test, while the qualitative data were analyzed using content analysis. The quantitative results reveal a positive change in the science teachers' orientations towards inquiry-based instruction. However, the qualitative results suggest that this change occurred only in the particular context where the science teachers focused more on students' learning than on the instructional objectives and classroom management issues. Thus, what and how students can learn in the context of inquiry-based instruction should be emphasized in the professional development for science teachers to adopt inquiry-based orientations.