Abstract: An economic order quantity (EOQ) model with payment in advance is developed to purchase high-price raw materials. A joint policy of replenishments and pre-payments is employed to supply the materials. The rate of demand and lead time are taken to be constant and it is assumed that shortage does not occur in the cycles. The cycle is divided into three parts; the first part is the time between the earlier replenishment-time to the next order-time (t0), the second part is the period between t0 to a payment-time (tk) and the third part is the period between tk to the next replenishment-time. At the start of the second part (t0), α% of the purchasing cost is paid. The (1-α)% remaining purchasing cost is paid at the start of the third part (tk). The cost of the model is purchasing under incremental discount for each order, clearance cost, fixed-order cost, transportation cost, holding and capital costs. Holding cost is for on hand inventory and capital cost is for capital that is paid for the next order. The constraints of the problem are space, budget and upper limit for the number of orders per year. Also lead-time is considered less than a cycle time. The model of this problem is shown to be an integer-nonlinear-programming type and in order to solve it, a hybrid harmony search algorithm approach is used. At the end, a numerical example is given to demonstrate the applicability of the proposed methodology in real world inventory control problems.