To understand how integrated science education (ISE) can be transferred into successful classroom practices, it is important to understand teachers' perceptions and self-efficacy. The focus of this study is twofold: (1) to understand how teachers perceive ISE and (2) to assess if science teachers' perceptions of and experiences with integrated education correlate with their views on self-efficacy in relation to ISE. Ninety-five Finnish science teachers participated in an online survey study. A mixed method approach via exploratory factor analysis and data-driven content analysis was used. Self-efficacy emerged as a key factor explaining teachers' perceptions of and their lack of confidence in implementing ISE as well as their need for support. In addition, teachers regarded ISE as a relevant teaching method, but challenging to implement, and teachers primarily applied integrated approaches irregularly and seldom. Furthermore, teachers' experiences with integrated activities and collaboration correlated with their views on integrated education and self-efficacy. These findings indicate teachers need support to better understand and implement ISE.