The aim of this study is to determine EOQ model for finding the optimal order quantity of retailer’s inventory system with finite replenishment rate under trade credit period depending on the order quantity. For determining this EOQ model that gives a minimum total cost per unit time, the algebraic method is formulated function of total cost per unit time to be completing the square form of the order quantity. In addition, theoretical and numerical results under trade credit period depending on the order quantity are shown that the total cost per unit time varies inversely with trade credit period, that is, a long trade credit period gives a minimum total cost per unit. Keywords : EOQ model, finite replenishment rate, trade credit period