A mixed integer nonlinear programming model is presented to find the optimal replenishment policy for a particular type of product for the case of a single retailer and multiple potential suppliers. Each supplier offers all-unit quantity discounts as an incentive mechanism. Multiple orders are allowed to be submitted to the selected suppliers during a repeating order cycle. The demand rate is considered to be not constant but dependent upon the selling price. The model provides the optimal number of orders and corresponding order quantities for the selected suppliers, and the optimal demand rate and selling price that maximize the total profit per time unit under suppliers' capacity and quality constraints. A numerical example is presented to illustrate the results of the proposed model.