In this study, the effects of STEM activities on the problem-solving skills of preschool children were investigated. A two-group (study: n = 18 and control: n = 18) pre-test/post-test/retention test experimental design was conducted to collected data using a researcher developed General Information Form and an established Problem-Solving Skills Scale (4-7 years). The STEM activities prepared by the researcher were applied in the experimental group three days a week for eight weeks in addition to the National Education Program, whereas only the National EDUCATION Program was applied for the control group. As a result of the analyses, it was determined that STEM activities cause a significant difference in the problem-solving skills of 6-year-old preschool children (p < 0.05). The results showed that the effect of STEM activities on the problem-solving skills of 6-year-old preschool children is positive.