This paper aimed to explore how pedagogical content knowledge (PCK) of teachers influenced their adaptations of the curriculum materials of the new senior secondary chemistry curriculum, a standards-based science curriculum, in China. This study was based on the premise that the interaction of the teacher with the curriculum materials determines what happens in the classroom. An interpretive approach was adopted and five experienced chemistry teachers in four senior secondary schools participated in this study. Classroom observations and interviews were used as research methods. The data analysis revealed that there were four components of PCK that led to teachers' adaptations of curriculum materials and they were knowledge of students' understanding of science, knowledge of assessment in science, knowledge of instructional strategies, and knowledge of science curriculum. Among these four components of PCK, knowledge of students' understanding of science and knowledge of assessment in science were the factors that most influenced teachers' adaptations of curriculum materials. Furthermore, the ways that these four components of PCK influenced teachers' adaptations were different. The implications of the findings and the suggestions for the further studies were discussed in the last section of this paper.