Abstract <p>German science teachers often teach interdisciplinary science without being specifically qualified for interdisciplinary science teaching. Instead, they study one or two science-subjects out of biology, chemistry, and physics. Hence, science teachers need out-of-field teaching expertise within the sciences for interdisciplinary science teaching in Germany. We developed a questionnaire on self-rated content knowledge based on an interdisciplinary science curriculum for lower secondary education. Self-rated content knowledge is investigated as it is a proxy for actual content knowledge and a part of science academic self-concept. </p> <p>We surveyed 312 German pre-service science teachers to find out, to what extent they feel prepared to teach science interdisciplinarily. We confirmed the reliability and the validity of the questionnaire for self-rated content knowledge. We identified three disciplinary science-subject-related factors corresponding to biology, chemistry, and physics in a confirmatory factor analysis. Pre-service teachers, who studied different disciplinary science-subjects varied in their self-rated content knowledge for those three factors. They rated their content knowledge the highest for the subject they studied. Pre-service biology teachers’ self-rated content knowledge related to non-studied science-subjects was the lowest compared to all other groups. Our hypothesis that self-rated content knowledge for out-of-field science-subjects is more challenging for higher than for lower school years was only partially confirmed. Instead, disciplinary educated pre-service teachers displayed a more differentiated pattern depending on the subjects and school years. The paper argues for further developing interdisciplinary science teacher education in and beyond Germany.</p>