商品如損壞、揮發或變質等現象稱為退化，常見具退化性商品如蔬菜、水果及藥物等會有退化性問題產生。而供應商為增加零售商的訂貨量，有時會提供信用交易來刺激買氣，在信用交易週期內零售商將不用支付利息給供應商，但供應商提供較長的信用交易週期亦提高違約的風險。本文中提出一經濟訂購量存貨管理模型，主要探討零售商所訂購的商品具有退化性，另外商品的需求率考慮與信用交易週期及售出價格有關。文中將針對探討的模型提出定理來找出最適的訂購週期、售出價格及信用交易週期，使得整個訂購週期內具有最大的平均利潤，其後並以例題說明本模型。

Deterioration is defined as damage, evaporation or decay that prevents items from being used for its original purpose. Some examples of items that deteriorate are vegetables, fruits, pharmaceuticals and others. To increase sales, a supplier frequently offers retailers a trade credit period to promote the purchasing amount. There is no interest charge to retailers if the purchasing amount is paid within the credit period, but granting a long credit period from a supplier increases default risk. In this paper, we propose an economic order quantity inventory management model for items with deterioration and demand rate is a function of credit period and selling price. We then characterize the retail's optimal ordering period, selling price and credit period. Finally, we run numerical examples to illustrate the model we proposed.