<p>Interdisciplinary competence is crucial for understanding and addressing real-world scientific challenges. This study seeks to assess students’ interdisciplinary competence in the context of chemistry and biology. To this end, this research constructed a framework to describe students’ interdisciplinary competence, which contained four components, each with three performance levels. Guided by this framework, an instrument comprising 17 constructed-response items centered on three scientific tasks was developed. A total of 293 high school students took part in the test in Shanghai, China. Results of partial credit Rasch analysis supported the instrument’s satisfactory reliability and validity. The majority of students achieved the advanced level of interdisciplinary identification, while nearly half of the students only attained the basic level of critical evaluation, knowledge integration, and interdisciplinary production. As the complexity of competence components increased, the percentages of students achieving advanced levels demonstrated a progressive decline. Furthermore, most of the students performed unbalanced across the four components. Implications for interdisciplinary science education and the possible applications of the new instrument were also discussed.</p>