In this paper, we examine the retailer’s information sharing decision in an authentic supply chain with a single supplier and a single retailer under different counterfeiter encroachment situations. We propose a Stackelberg game model to analyze the optimal wholesale price of the supplier, the optimal order quantity of the retailer and the optimal production quantity of the counterfeiter. We obtain the information sharing strategies of the retailer and analyze the impact of the counterfeiter on the authentic supply chain. It is revealed that: (1) under certain conditions, the retailer will voluntarily share information with the upstream supplier and (2) the existence of the counterfeiter may increase the profit of the authentic supply chain.