Project Portfolio Selection (PPS) is a kind of problem found in a variety of practical situations, such as research and development planning. Several different approaches have been proposed to deal with Project Portfolio Selection (PPS). However, the consideration on benefits synergies between projects is little addressed in the literature. The main focus of this paper is on synergy between projects, which is related to the interactions between the benefits of the projects. In this paper, a method has been developed to meet some of the major limitations of existing models: the inadequacy of the treatment of multiple criteria and inter-relationships between projects and the absence of the recognition and incorporation of managers' experience and knowledge, concerning to synergy between projects. The decision model is formulated as a non-linear 0-1 optimization problem, which considers the evaluations of projects and the benefit synergies of theses projects.