Several conceptual and theoretical studies on the importance of science-technology-engineering-mathematics (STEM) careers and the 21st century skills required for these careers have been carried out; because they have been accepted as important for the improvement of society and maintenance of economic growth. However, there has not been research within the current educational literature examining the relationship between 21st century skills and STEM career interests of middle school students. Therefore, the main aim of this study is to examine the presence and level of the relationship between middle school students' 21st century skills and their interest in pursuing a STEM career. In addition, the presence of significant differences between male and female students' STEM career interest and 21st century skills was also investigated. The participants of the study were 282 middle school students. The research was completed via a quantitative study based on the relational survey model; data collection tools were STEM career interest survey and 21st century skills scale. A Pearson product-moment correlation method was used to explore the presence and level of the relationship between students' 21st century skills and STEM career interest. In addition, an independent samples t-test was used to answer whether there are significant differences between students' STEM career interest and/or 21st century skills in terms of gender. The findings showed that there is a statistically significant relationship between students' 21st century skills and STEM career interest. In addition, there is not a significant difference between female and male students' STEM career interest, while there is a significant difference between their 21st century skills.