Integrated Science, Technology, Engineering and Mathematics (STEM) education is an emerging approach to improve students' achievement and interest in STEM disciplines. However, the implementation of integrated STEM education depends strongly on teachers' competence, which entails, among others, teachers' attitudes. Nonetheless, not much is known about the factors that influence teachers' attitudes toward teaching integrated STEM. Therefore this paper uses a survey method to get insight into the relationship between three groups of variables and teachers' attitudes toward teaching integrated STEM: teacher background characteristics, personal attitudes and school context variables. The results of the multiple regression analyses reveal three variables that are positively linked with teachers' attitudes: professional development, personal relevance of science and social context. Moreover two variables show a negative correlation: having more than 20 years of teaching experience and experience in mathematics. The results of this study provide valuable information about factors related to teachers' attitudes toward teaching integrated STEM. Moreover, these results can be deployed by school administrators to guide them when implementing integrated STEM education in their school.