In today's world, businesses require consistent and stable supplier networks to maximize their profits, to grow healthy and to stay permanently in the market. This study aims to select and evaluate suppliers and to constitute accurate pricing mechanism by considering the most appropriate criteria for a public institution which executes the purchasing activities in public sector. Towards this goal, the criteria and sub criteria that affect the process of supplier selection and evaluation for the institution, and the interactions between the criteria are determined by a survey study and statistical analysis. Criteria and sub criteria are weighted by Analytical Hierarchy Process (AHP). 32 suppliers are evaluated by PROMETHEE II which is a multi criteria decision making method. Suppliers are also evaluated based on each criterion which provides feedback for sources of differences among them during the purchase action. Furthermore the Stability Interval Analysis is performed to investigate impacts on the results of the changes in the weights of criteria determined by AHP. This study provides the minimization of economic losses that come from the inadequate evaluation of suppliers for the institution.