The purpose of this study is to examine changes in pre-service science teachers' entrepreneurship mindsets during engineering design-based activities. A holistic single-case study was used in the study. Twenty-eight pre-service teachers carried out engineering design-based activities (five weeks, 20 hours) in the science teaching laboratory practices course. The pre-service teachers' use of Entrepreneurship Mindsets (EM) in solving the water pollution problem during engineering design-based activities was examined in this study. Data were collected via engineering design challenge worksheets and public service announcements. The data were analyzed with the Extended KEEN Student Outcomes (eKSOs) rubric. Frequency tables were created in line with the sub-dimensions of EM (curiosity, connections, creating value, communication, character, and collaboration). As a result of the research, it was found that the pre-service teachers mostly used curiosity, connections, and creating value during the water treatment and wastewater assessment plant design process. Engineering is an important context for the development of EM as it creates various contexts that contribute to the development of these mindsets in pre-service science teacher education.