The relationships between the members of supply chain were modeled in many researches, such as cooperative and non-cooperative situation. In our paper, the main question is how much and for which price should each seller offer her product to maximize the profit. In the proposed methodology, Bi-level programming is used for modeling and then GAMS (general algebraic modeling system) language for solving the problem. In the presented model, the first level, called upper sub-problem and supposed as leader is trying to maximize each seller profits by obtaining the optimal offered quantity of individual seller. The objective of follower (buyer) is at second level. The lower sub-problem uses the results of the seller's model and then maximizes its profit. These optimizations are obtained with regard to the some other constraints. Similar the other game theories problems, the Nash equilibrium point(s) is (are) the optimum decision of this seller-buyer supply chain. A numerical example is employed to illustrate the application of the proposed method. Keywords: Bi-level programming, Nash equilibrium, seller-buyer, supply chain management 1. Introduction In recent decades, big changes happen in different industries, so more competition is observed in selling markets. Each members of supply chain such as seller and buyer will try to maximize its own profit or on the other hand minimize its costs. In seller-buyer models, the seller produces a product, and after that in a wholesale price sells that to the buyer. Buyer in her turn retails the mention product to the consumer (Yang & Zhou, 2006; Chen et al, 2006;Dai et al, 2005) A wide literature exists on the suppliers' competition and their strategic choices. In categorizing the strategic behavior of seller-buyer supply chain, it could be falls into game theory decision making. Nash equilibrium is one of the solutions which are accepted by all players. Also, using this solution concept is very common. Hence, at first the profit of each seller will be calculated in different possible strategy. Then, after considering the buyer conditions Nash equilibrium points and its optimum selected strategy of each seller would be found. On the other hand the proposed method is a seller selecting with regard to the parameters, decision variables and objects functions of not only sellers but the buyer. Generally, each seller are intended in selling its products as high as it is possible, but exist competition forced seller to offer acceptable prices. The strategy of offering prices of seller depends on other seller (the opponents) behavior, total demand and many other factors. For a seller, it is so significant and critical to select a good price choosing strategy according to its opponents' behavior and other conditions. Hence, it's better for sellers to solve their problem by game theory. The game based methods, which will be used in this article, are more useful in solving these problems. The game based problem solutions can be classified as follows in (Soleymani et al, 2007;Ferr...