The major purpose of this study was to describe a science teacher's views of STS (Science–Technology–Society) instruction and what she acquired after implementing a two-semester STS-oriented science course in a high school of Taiwan. Upon analysis of the teacher's journals, interview data, concept maps, and relevant student questionnaire responses, this study revealed the following findings. The teacher believed that STS instruction was a potential way of practicing so-called “constructivist” teaching and her pedagogical knowledge about STS showed a considerable growth. As a result of STS instruction, her epistemological views of science seemed to progress toward more constructivist-oriented views of science. The heavy content load of Taiwan's national curriculum, regular cross-class standard tests, the lack of peers' or administrative support, the resource limitations in Chinese language, and the cultural impacts were identified as major factors that inhibited her implementation of STS instruction. © 2001 John Wiley & Sons, Inc. Sci Ed86:23–41, 2001.