Nowadays, due to the importance of competition in supply chain, supplier selection is one of the most important issues in competition between manufacturers. Different companies take various criteria into account to select the appropriate suppliers. In this paper, we study a supplier selection problem, considering three key criteria: price, quality and delivery performance. For the first time in this paper a single-echelon supply chain has been studied at which each manufacturer tries not only to optimise his/her own situation but also to remove the other buyers from their optimum points. Hence, this paper considered a new competitive supplier selection problem with some assumption according to real world. In addition, because of new assumptions and complexity of the studied problem, an Imperialist Competitive Algorithm has been used to solve the problem. Finally the success of the mentioned model will be supported by a numerical example and the difference between decision making in competitive and non-competitive market will be shown.