This paper ,on a basis of total acquisition cost , establishes a model for deciding the optimal number of suppliers when a buyer purchases a component in a co2opetition environment . The model comprehensively describes factors that influence the total acquisition cost of the component . These factors include market environment , compo2 nent characteristics , price stability , profit margin , relative bargaining power between the buyer and its suppliers , the degree of co2opetition and coordination costs , etc. By using numeral examples ,we illustrate how these factors af2 fect the optimal number of suppliers