Recent literature emphasizes the importance of viewing teaching as a knowledge-building practice and teachers’ capacity for knowledge creation and innovation. Therefore, this study aimed to develop languages student teachers’ pedagogical content knowledge for their target language teaching through a double stimulation design using video-based learning modules. The second aim of this study was to develop pre-service teachers’ epistemic agency in creating ideas in their languages teaching design. Epistemic agency refers to their intention and capacity to generate new ideas in their teaching design. In the first phase of design, a problem in language teaching, such as how to teach pronunciation, was presented as the first stimulus to active students’ existing knowledge. In the second phase, the second stimulus, a short video-clip containing an experienced teachers’ teaching demonstration as a resolution to the problem was provided to pre-service teachers for them to work out their own way to resolve the problem and further develop it in their design of an e-resource for teaching their target language. The study was conducted in a secondary languages teacher education program in an Australian university. The data included pre-service teachers’ participation in the video-based module which was evidenced by the audio-recorded group discussion and written discussion worksheets, and retrospective assignment analysis. The findings revealed the factors impacting on pre-service teachers’ epistemic agency include their interaction with the stimulus, their group collection construction of ideas, and their interpretation of the mediating tools.