The aim of the present study was to investigate the development of technological pedagogical content knowledge (TPCK) and Web 2.0 rapid content development self-efficacy beliefs (W2SEB) and to determine the relationship between them for middle school pre-service mathematics teachers through their involvement in a course designed using a Web 2.0 tools. To achieve this aim, thirty pre-service teachers participated in 42 hours of course in which they could interact with Web-based applications. In this course, a variety of Web 2.0 tools were introduced and pre-service teachers were requested to develop and present e-content related to the use of these applications for learning outcomes determined in mathematics teaching. In order to collect the required data, the TPCK and W2SEB scale were applied to pre-service teachers at the beginning and end of the course. The data obtained from the scales were quantitatively analyzed. Within the scope of the activities, while there were positive developments in terms of the technological pedagogical knowledge levels and self-efficacy beliefs, there was a significant relationship identified between them. Additionally, when the regression results related to the post-test are investigated, the TPCK components of technological and mathematical knowledge were shown to be significant predictors of Web 2.0 rapid content development self-efficacy beliefs.