Since IT Outsourcing has been popular, the competition among IT service providers became to be intensified as winning contracts is the critical success factor for them. Thus, this paper identified the factors that influence the selection of IT service providers via the related literature review and in-depth interviews with related experts with more than 10 years of rich experience in the industry. The review and interviews resulted in the establishment of the AHP analysis model consisting of 5 criteria with 17 sub-criteria. Based on the analysis of the data collected from this research, the sub-criteria were weighted and the characteristics of the IT service industry were reflected, indicating that the sub-criteria of high importance were applied strategically depending on various environmental characteristics.