Project management is critical for the success of the large and complicated IT project. Accordingly, to improve the efficiency of the project management, operation of separate Project Management Office (PMO) organization is getting important. Despite the appreciation of PMO as necessary for project success, the result has not always been positive. In this respect, we intended to formalize the PMO success model by incorporating necessary factors related to PMO services and capabilities, and their relationship. Empirical testing results verified critical antecedents comprising PMO services, which included schedule, quality, budget and others. Furthermore, moderating impacts of PMO capabilities are quantitatively assessed. The research findings offer practical insights for successful management of PMO.