The purpose of this study was to develop and validate a scale to measure perceived loafing in group projects among college students. In this study, “perceived loafing in group projects” refers to the extent to which an individual student perceives that their peers are not participating diligently in group tasks. A literature review was conducted, and data from focus group interviews with 12 college students, a pilot survey with 200 students, and a main survey with 300 students were analyzed. The main findings of this study are as follows. First, based on the literature review and focus group interviews, 12 preliminary items were developed to measure perceived loafing, reflecting aspects of insufficient communication and lack of diligence in task performance in group projects. Second, the pilot survey items were finalized after content validation by experts. Third, the analysis of the pilot survey indicated that the scale for perceived loafing in group projects among college students was identified as a single factor, and eight items were confirmed as the final items. Fourth, the main survey analysis showed the scale’s reliability to be .92, supporting its internal consistency and providing evidence for construct (convergent) validity. Furthermore, criterion-related validity was confirmed by conducting correlation analyses between the newly developed scale and related variables, such as group cohesion, collective efficacy, academic engagement, academic disengagement, and an existing perceived loafing scale. The present study is significant in that it develops and validates a scale that measures perceived loafing in group projects among college students, improving upon the limitations of existing scales. This newly developed scale serves as a foundational tool for understanding and managing perceived loafing in university group projects.