In this study, an instructional programme was designed and implemented with preschool teachers to teach them about integrated STEM education. This paper focused on how this instruction changed teachers' perceptions of engineering. The study aimed at exploring what the teachers learned about engineering, one of the STEM disciplines, throughout their exposure to this programme. Thirty teachers participated in the study. Data was gathered via a drawing test and participants' diaries. For the analysis of the drawing test, a numerical coding system developed by Thompson and Lyons (2008) was used. Thematic content analysis was used for the qualitative analysis of the drawing test and the analysis of participant diaries. It was indicated that professional development experience enhanced pre-school teachers' perceptions of engineering. It was found that this programme helped teachers realise their deficiencies in relation to their engineering perceptions of engineering and rectify them. It was found that this professional development experience had positive effects on learning content knowledge in a specific engineering discipline and supporting positive feelings towards engineering.