The paper aims to fill the gap of investigating the role of project management offices at organizations of different project management maturity levels and to introduce a model developed by the author that integrates strategic management, project management and knowledge management in order to set up the strategic project portfolio and to support the successful planning and realization of strategic projects. Nowadays we deal with projects in several areas of life. Large infrastructural investments – subway, bridge, railway, or highway reconstruction, building residential communities – are completed in projects. Large enterprises start projects to develop new products, services and to introduce them to the market. Project is also one of the often used terms regarding the planning, organizing and hosting of international sport and cultural events. The culture of projects is not only spreading rapidly in the last few years among small- and medium-sized enterprises and the public sector in the member states of the European Union, but the project management methods, techniques, and related knowledge used during the project life cycle are also of extreme importance. Nowadays, we are working and living among projects. These projects have become part of the organizational strategy, and project management is an integral part of strategic management. The purpose of strategic projects is to contribute to the realization of the organizational strategy and to help the implementation of strategic goals. The main question is on the one hand how these projects are selected in order to have the project portfolio that is aligned with the organizational strategy and on the other hand how knowledge management centers like Project Management Offices (PMOs) can support the management of selected projects. The relevance of the research is highlighted by the PM Solutions’ “State of the PMO” study (2014, 2016), according to which PMOs garner more attention at the executive level and their role in strategic functions increases. Besides, PMOs have been significantly engaging in portfolio management functions. The paper first gives an overview about the theories of single project management and the organizational project management, and introduces the modified and further developed model of Kessler and Winkelhofer (1997) called “project oriented strategy planning” (Szabó, 2012). This is followed by the analysis of organizational project management maturity models. Then the role of PMO in selecting strategic projects is introduced and discussed. In the practical part of the paper an empirical survey is presented. The role of PMOs are analyzed at organizations with different project management maturity levels.