This research aimed to introduce a STEM activity specifically prepared in accordance with the engineering design process and to examine a group of prospective preschool teachers' views about the activity. A total of 16 prospective teachers studying in the final year of a public university in the West Black Sea Region, Turkey, during the fall semester of the 2021/22 academic year were the participants of the study. The STEM activity was based on the problem of making a fish model that can sink, swim and float in water. At the end of the activity, an open-ended activity opinion form was used to gather the prospective teachers' views about the activity. The data were analyzed using the descriptive analysis method by taking into consideration the themes related to STEM, as specified in the theoretical framework. The results of the study show that the prospective teachers took the opportunity to experience how a STEM activity is held, that they found the activity fun and interesting, as well as conducive to learning science concepts and higher-order thinking skills. As for the negative aspects of the activity, the respondents stated that the activity was time-consuming, and that it was difficult to decide on and build the design. We believe that this study will provide theoretical and practical contributions to both researchers and preschool teachers.