There has been a recent increase in studies devoted to integrated science, technology, and engineering mathematics (STEM) education. However, as the field is emerging, there has not been a large amount of scholarship on how to best provide teacher professional development (PD) on integrated STEM education. On the other hand, well-grounded research is available in the field of effective teacher professional development. Therefore, in this study, a systematic review of empirical studies on training elementary/primary school teachers in integrated STEM education was undertaken. Using an adapted version of Lawless and Pellegrino's analytical framework (2007), the emerging commonalities among eleven studies in conjunction with the literature on effective teacher professional development were analyzed and discussed. This study aims at connecting current STEM-integrated PD activities with the literature on effective PD and laying the groundwork for future professional development programs and evaluations in integrating STEM subject areas in elementary or primary schools.