Abstract: The main purpose of this study is to investigate the case where the retailer`s unit selling price and the purchasing price per unit are not necessarily equal within the EPQ framework. Under these conditions, we establish the retailer`s inventory system as a cost minimization problem to determine the retailer`s optimal inventory cycle time and optimal order quantity. Three easy-to-use theorems are developed to efficiently determine the optimal inventory policy for the retailer. Some previously published results of other researchers are deduced as special cases. Finally, numerical examples are given to illustrate these theorems obtained in this study.