We propose project evaluation criteria by considering not only the Six Sigma approach, but also European Foundation for Quality Management (EFQM) model features, and introduce an evaluation model for completed Six Sigma projects. The proposed model uses seven main criteria: leadership, policies/strategies, main performance results, social results, employees, cooperation, and resources. These main criteria are enhanced by 18 sub-criteria. Due to the evaluation scale being based on human judgments, fuzzy set theory is an obvious methodology choice to account for uncertainty in the evaluation data. Type-2 fuzzy sets can provide flexibility for uncertainty by considering membership functions and their footprints. We also propose an evaluation methodology for weighting the main and sub-criteria and for ranking completed Six Sigma projects through a fuzzy analytic network process (ANP) method with interval type-2 fuzzy sets. From our analysis, performance results were found to have the highest weight among the seven main criteria, while achieving project objectives was found to be the most effective criteria.