The influence of the flow-rate ratio (m-value) on the startup and the cyclic steady-state performance of the simulated moving bed (SMB) process were studied under the condition of a fixed feed flow rate. Each system was evaluated from the viewpoint of four performance parameters (major product concentration, purity, eluent consumption, and productivity). Flow-rate ratios of zones II and III (m(2) and m(3)) played key roles in the startup and cyclic steady-state behaviors of the performance parameters compared to m-values of zones I and IV (m(1) and m(4)) in the four-zone SMB process. However, the performance parameters were steeply changed near the operating boundaries of m, and m(4) even though their variation was smaller than the results from m(2) and m(3). In addition, the effects of m(1) and m(4) on the major product concentration were substantial in the operating range. The startup periods of both product concentrations were increased as the operating point in the triangle region became far from the diagonal in terms of m(2) and m(3). On the other hand, the variation of m(1) and m(4) could lead to a change in performance without any adjustment to the startup period. (c) 2008 Elsevier B.V. All rights reserved.