The aim of this work is the identification of software project quality performance measures that would enable valid comparison and ranking of the completed projects. Software projects can be characterized by a set of influence factors. A subset of the influence factors is relevant for software project quality. In order to predict and determine the ranking of software projects by their success, and thus present a valid software project quality performance measure, we employ Grey system theory. Grey relational analysis is a kind of method which enables determination of the relational degree of every factor in the system. The method can be used for systems that are incompletely described with relatively few data available, and for which standard statistical assumptions are not satisfied.Relational degree between seven relevant software project quality influence factors is calculated for a set of ten software projects. The results demonstrate the usefulness and applicability of the Grey system theory in software project quality assessment.