Chemical representations play an important role in helping learners to understand chemical contents. Thus, dealing with chemical representations is a necessity for learning chemistry, but at the same time, it presents a great challenge to learners. Due to this great challenge, it is not surprising that numerous national and international studies have shown that students have remarkable difficulties. Since most of the studies regarding chemical representations have focused on investigating high-school students' knowledge so far, little is known about university students' and especially student teachers' knowledge. The latter group is additionally challenged by the necessity of learning how to transform their own knowledge in order to teach chemical representations to their prospective students. Given this as a starting point, a paper-and-pencil test with 19 items in both semi-open and closed format was developed to investigate the extent of student teachers' knowledge of chemical representations. The present paper describes the design, validation, and psychometric analysis of this test instrument – the so-called Chemical Representations Inventory (CRI). The CRI includes a variety of chemical representations and chemical contents on both high-school and university level. Both classical test theory and Rasch modelling were used for the analysis. In addition, a qualitative analysis was performed, and factors which possibly influence the item difficulty were identified. Even though the CRI was originally developed for a sample of student teachers, it can also be used to measure chemistry students' knowledge on a basic level.