Purpose. This study aimed to develop a group organizational learning activity inventory for evidence-based practice (EBP) institutionalized by hospitals and to verify its reliability and validity. Methods. A draft inventory was created after verifying content and face validity of draft items developed based on interview data and materials used in EBP implementation. Construct validity and reliability were assessed cross-sectionally through an anonymous self-administered survey conducted via web and printed questionnaires. Construct validity was confirmed using exploratory and confirmatory factor analyses, and internal consistency and convergent/discriminant validity were verified. Inventory structure was determined using the theoretical model based on the hypothetical constructive concept. Temporal stability was assessed two weeks after the initial survey. Result. A draft inventory comprising 12 factors and 47 items was created based on 95 draft items. Data from 371 nurses across 55 departments in 12 hospitals were analyzed. The inventory comprised 8 factors and 40 items based on the theoretical model. The comparative fit index was 0.86, the Tucker–Lewis index was 0.85, the root mean square error of approximation was 0.09, and standardized root mean square was 0.04. Cronbach’s alpha of each factor was ≥0.8, and the temporal stability was moderate. Conclusion. We developed the group organizational learning activity inventory, comprising 8 factors and 40 items. Though construct validity was low, the reliability and concurrent/convergent validities were confirmed. This inventory contains new factors that measure the group activities to ensure EBP’s continuation in hospitals: forming common knowledge, understanding the value of EBP in groups, and fostering ownership thereof. Using this inventory, departments that introduced EBP can evaluate the extent of activities leading to nurses’ continuation of EBP and find the improvement point.