In the context of a two-echelon supply chain with one manufacturer and many retailers which are engaged in a Bertrand competition and have some private information of demand, the information sharing has been investigated by using game-theoretical concepts. The analysis suggested that the information sharing can increase the profit of the whole supply chain and the manufacturer but it also decreases the retailers' profit. This makes the retailers have no incentives to share their demand information to the manufacturer. So, no information sharing is the unique equilibrium in this game