This paper seeks systematic inventory management approaches to the purchase-dependent demands in the joint replenishment problem (JRP) that handles multiple items. It is not easy to accurately derive the objective function of the JRP inventory model in the presence of purchase dependencies. In additions, finding the optimal solution of the JRP inventory model is not easy. Thus, we first derive the conditions of the optimal solution by analyzing the properties of the inventory model through the JRP EOQ model considering the purchase-dependent demands. Then we extend the results to JRP periodic review inventory model. Through computer simulations, we review how effective the approach of this research is, and conduct an in-depth analysis of inventory policies, depending on the degree of purchasing dependency. The computer simulations show that the JRP inventory policy considering the purchase dependencies generates less total cost than the JRP inventory policy ignoring the purchase dependencies.In general, JRP inventory policies considering purchase dependencies reduce sales losses by having more inventory and result in lower total costs.