The aim of this study was to reveal the changes in metaphorical perceptions of teachers received STEM course towards STEM and 21st century skills. This study adopted an instrumental case study to find out the change in teachers' metaphoric perceptions of STEM and 21st century skills. The changes in teachers' perception of STEM and 21st century skills were tried to be reflected by using metaphors. The data of 24 teachers were included in the study group in order to obtain qualified data. Using the metaphor form developed by the researchers, data on STEM and 21st century skills were collected from 24 teachers. The data was collected from the participants and analyzed separately by two researchers by using content analysis method. Afterwards, researchers came together with the third researcher and the similarities and differences of the analyses were determined. Considering these similarities and differences, the reliability coefficient of the study was calculated and found 0.75. The metaphors and conceptual categories obtained as a result of the research show that teachers created limited metaphors for their knowledge of STEM and 21st century skills before STEM course, while they created more comprehensive metaphors for STEM and 21st century skills as a result of their awareness and knowledge after STEM course.