The purpose of this study is to investigate the effects of STEM activities on preservice elementary teachers' STEM awareness, science teaching self-efficacy beliefs and inquiry skills. The pretest/posttest control group design, which is one of the quasi-experimental designs and quantitative research techniques, was used in the study. The sample of the study was composed of a total of 60 pre-service elementary teachers (40 were in experimental, 20 were in control group). The participants were enrolled in a Science Teaching course in 3rd grade of Classroom Teaching program in the first semester of 2019-2020 academic year in Siirt University Elementary Education Department. At the beginning of the study, STEM approach and application steps to apply STEM activities were introduced to participants in experimental group. Then preservice elementary teachers prepared their own STEM activities (cars, ship models, camping, bridges, catapult, robot models, sound instrument) and presented to the other participants. In the control group, traditional approach of Science Teaching course was applied ("teaching methods and strategies that make students active in science teaching", "science and engineering practices", "STEM education and technology integration", "project-based learning and STEM education"). . The activities took place 8 weeks. "STEM Awareness Scale", "Self-Efficacy Belief Scale in Science Teaching" and "Inquiry Skills Scale" were applied as pretest and posttest. The data were analyzed using independent samples t-test. As a result of analysis, it was found that statistically significant difference in favor of experimental group on the sub-dimensions of STEM awareness and inquiry skills. There was no statistically significant difference on self-efficacy points. Within this context, it was concluded that STEM activities positively affect STEM awareness and inquiry skills.