The call for the implementation of integrated science, technology, engineering, and mathematics (iSTEM) teaching has been on the rise. This teaching approach helps students to develop innovative skills and meet twenty-first century challenges. However, teachers need to possess positive attitudes toward iSTEM teaching to implement it. Therefore, studying factors that influence these attitudes is important. So far, investigated factors have focused on teachers' personal and professional experiences. Predisposing and enabling factors related to iSTEM teaching are yet to be investigated. One putative construct that includes predisposing and enabling factors is adaptive expertise (AE) which allows professionals to highly perform in new tasks. Here, we argue that AE in science teaching is linked to teachers' iSTEM attitudes through its three dimensions: perceived relevance (PR), self-efficacy (SE), and anxiety (Anx). We utilized a cross-sectional survey method to verify the proposed relationship on fourth year preservice primary science teachers (n = 91). They completed two online surveys measuring AE in science teaching and iSTEM attitudes, respectively. Results from multivariate regression modeling indicate a significant positive effect of AE in science teaching was found significantly positive on all three dimensions of iSTEM attitudes. These findings draw teacher educators' attention to the importance of developing adaptive expertise while preparing iSTEM teaching advocates.