The trend of avoiding science, technology, engineering, and mathematics (STEM) majors has persisted resulting in a lack of professionals in STEM fields. Further, the current STEM education system in Korea does not meet domestic demands for STEM labor. To discover an educational approach encouraging students to choose STEM majors at the post-secondary level, the current study employed a survey instrument investigating students’ attitudes toward STEM project based learning (PBL), and examined the relationships between these attitudes and intent to pursue a STEM major. A model depicting the relationships was proposed, and the structure of the model was verified using structural equation modeling. Additionally, a mediation relationship on the model was investigated and tested. Finally, the gender difference on the paths of the structural model was analyzed using multiple-group analysis. The results indicated that students who were positive toward PBL components (i.e., technology based learning, self-regulated learning, and hands-on activities) except “collaborative learning” were more likely to have the intent to pursue a STEM PBL. In addition, belief in STEM majors’ benefit played a role as a mediator. The findings of this study help secondary teachers guide students through major and job selection by integrating PBL into mathematics and science classrooms.