Disengagement is considered a significant component that affects the success, participation, and activity of the students in the online course. Reviewing the literature revealed the lack of a measurement tool for assessing students' disengagement in online courses. This study aimed to develop a scale that examines student disengagement in online courses through validation and reliability studies. The study was conducted with 772 undergraduate students who took an online course during the study. Exploratory factor analyses revealed that nine items were extracted under one factor with an eigenvalue >1. Confirmatory factor analysis (CFA) validated the one-factor model, showing significant factor loadings, and adequate fit indices. As a result, the scale of disengagement in online courses met the validity and reliability criteria. The disengagement in online courses scale can be used to examine the precedents and antecedents of disengagement in a variety of online learning settings.