Nowadays, many organizations adopt Information Technology Service Management (ITSM) best practices to enhance their IT service related processes. Although many organizations have adopted ITSM frameworks such as Information Technology Infrastructure Library (ITIL), not all have been successful. Keeping this in mind, this paper seeks to identify Critical Success Factors (CSFs) that impact on successful implementation of ITSM frameworks with a focus on ITIL in Iranian organizations as a case of a developing country. Hence, based on a mixed method, at first, with the semi-structured interviews and literature review, 22 success factors were identified. Following that, a questionnaire was developed and sent out to domain experts. Next, robust Exploratory Factor Analysis (EFA) was run for analyzing data and establishing construct validity which finally classified critical success factors into five groups named as “organizational”, “human resources”, “project management”, “managerial” and “process”. The findings of this study have provided a very useful reference for IT standardization scholars and practitioners to identify the important issues of ITSM frameworks implementation projects in their research and practice.