Proof has an important place both for the learning and teaching of mathematics. Pre-service mathematics teachers who learn about proof during undergraduate courses will use proofs during their teaching when they enter the profession. This is why the pre-service teachers’ views about proof are important. In this study, the effects of an intervention study that aims to improve pre-service mathematics teachers’ content and pedagogical content knowledge of proof on pre-service teachers’ views about proof were examined. The quantitative phase of this design-based research study was conducted in a teacher preparation program at a state university in Istanbul with 22 pre-service mathematics teachers, and the qualitative phase was conducted with three pre-service teachers. Data from the study were obtained during the spring semester of the 2017-2018 academic year. The quantitative data of the study were collected by a Likert-type scale, while the qualitative data were collected by semi-structured interviews. For the analysis of quantitative data, Two tests, Wilcoxon signed ranks test and marginal homogeneity test, were used. For qualitative data analysis, descriptive analysis was used. The quantitative findings of the study revealed that course intervention had a significant impact on pre-service teachers’ views about proof. The qualitative findings of the study also support quantitative findings. According to the qualitative findings of the study, the non-positive views of the participants before the implementation changed positively after the implementation. In line with the findings of the research, it may be suggested to conduct intervention studies to improve the different affective behaviors of pre-service teachers related to proof.