The main purpose of this study was to develop an instrument that assesses university students' perceived readiness for computer-supported collaborative learning (CSCL). Assessment in CSCL research had predominantly focused on measuring "after-collaboration" outcomes and "during-collaboration" behaviors while "before-collaboration" assessment was rarely studied. Given the nature of high learner agency and self-directness necessary in CSCL contexts, it was assumed that a sufficient level of student readiness for CSCL could promote positive attitudes and behaviors during the collaborative learning process and subsequent learning outcomes. Considering the importance of a before-collaboration status, this study proposes the new notion of students' readiness for CSCL (SR-CSCL) and presents a set of criteria to theoretically define and empirically measure the perceived level of SR-CSCL. Drawing on prior research on CSCL and readiness issues, we developed the SR-CSCL instrument with a three-dimensional framework consisting of: (a) motivation for collaborative learning, (b) prospective behaviors for collaborative learning and (c) online learning aptitude. The SR-CSCL instrument was validated with the university students in China in the pilot study (N = 120) and the main study (N = 295). Overall, the results showed some evidence of reliability and validity for the proposed instrument. This study presents an empirical assessment tool that can help instructors and researchers better understand and investigate how to assess and increase students' readiness levels in order to enhance their learning experiences in CSCL environments.