In the stage of optimizing a simulated moving bed (SMB) process for continuous separation, the extent of product concentration can sometimes be as important as the other performance criteria such as throughput and product purities. In such cases, the issue of maintaining the product concentration higher than a given target level needs to be taken into account during the SMB optimization. To investigate this issue, the throughput of an SMB process for binary separation was optimized in this study using a model separation system while placing a constraint on product concentration as well as pressure drop. The resultant throughput from such SMB optimization was highly affected by column length. It was found first that the throughput was limited by the constraint on the product concentration in the region of short columns but limited by the constraint on the pressure drop in the region of long columns. As a result, the optimal column length leading to the highest throughput occurred at the boundary between the product-concentration limiting region and the pressure-drop limiting region. In addition to the column length, the column configuration also played an important role in the optimization of the SMB with the constraint on the product concentration. As the target level of the raffinate product concentration was set higher, the optimal column configuration leading to the maximum throughput showed the pattern of placing more columns in zone IV. By contrast, the placement of more columns in zone I became the pattern of optimal column configuration when the target level of the extract product concentration was set higher. The results and methodology in this article will be useful when there is a necessity for developing SMBs that are to meet a certain requirement imposed on product concentration. (C) 2012 Elsevier B.V. All rights reserved.