The aim of this study was to determine the effects of 3D (3-dimensional) printing activities on pre-service teachers' self-efficacy in technological pedagogical content knowledge (TPCK) and their views of 3D printing activities. The study sample consisted of 39 students of science education, classroom teaching and preschool teaching departments of the faculty of education. An exploratory sequential mixed method design was used. In the quantitative part, a one group pre-test post-test design was used, and data were analysed using statistical methods. In the qualitative part, phenomenology was used, and data were analysed using content analysis. Results showed that 3D printing activities improved participants' self-efficacy in TPCK. Participants stated that 3D printers helped them develop skills in many areas and that 3D printer teaching materials contributed to both learning and teaching. The majority of participants had positive views on the effect of 3D objects on learning. They stated that 3D objects turned abstract concepts into concrete visual representations, facilitated learning, made lessons enjoyable, provided learning retention, encouraged them to learn more about their fields, increased their interest, and helped them develop creative thinking and design skills, and thus, create different content-specific educational materials.