Drawing upon the model for science teacher assessment literacy developed by [Abell, S. K., & Siegel, M. A. (2011). Assessment literacy: What science teachers need to know and be able to do. In "The professional knowledge base of science teaching" (pp. 205-221). Springer. https://doi-org.bibliotheek.ehb.be/10.1007/978-90-481-3927-9_12], this study explored science teachers' knowledge and practices of inquiry-based science instruction (IBSI) in Taiwan, and investigated the possible interactions among the categories of assessment literacy. Forty high school science teachers with relevant experience in IBSI participated in the study. Data were collected from semi-structured interviews and background questionnaires. We analysed the data and developed a coding scheme through both theory-oriented and data-oriented approaches. Four categories of teacher assessment literacy were explored, including assessment purposes, assessed learning outcomes, assessment strategies, and assessment scoring. The results indicated that, through formative assessments, teachers supported students' inquiry-based learning and self-regulated learning in a variety of ways. Furthermore, teachers not only used multiple data sources to assess students' learning performances, but also appreciated both subcategories of assessed learning outcomes - inquiry as means and inquiry as ends. The analysis also revealed some patterns of interactions among the categories of assessment literacy. Based on the findings, discussions and suggestions are provided.