In this research it is aimed to examine the effects of STEM-based activities on pre-service primary school teachers' scientific inquiry skills, conducted in a science education course of third year undergraduate students. A mixed research method, combining pretest posttest single group design and semi-structured interviews guided the study. Participants of the study consist of 47 pre-service primary school teachers in a state university. The activities implemented with third grade pre-service primary school teachers for ten weeks/thirty course hours. "Views About Scientific Inquiry" scale which was developed and translated into Turkish was used as data collection tool. Based on the eight aspects of science standards, a STEM activity plan was created for each of these dimensions in terms of science, mathematics, engineering and technology achievements. Test as pre and post-test are analyzed statically and for the normally distributed data of VASI, the dependent samples t-test was applied. The dependent sample t-test was used to determine whether there was a significant difference between the pre-test and post-test scores after the scientific method-based STEM applications. Semi-structured interviews were performed to support quantitative data and analyzed descriptively. Results of the study showed that at the beginning of the research, the scientific inquiry skills and views of the preservice primary teachers were inadequate. Additionally, there is a significant difference on scientific inquiry skills and views of the study group, participating in the STEM-based science activities, after STEM applications and activities within the course. It can be concluded that STEM based activities enhance scientific inquiry understandings and skills of pre-service primary school teachers.