In the present work, an asynchronous 3-zone simulated moving bed (SMB) has been constructed for the first time and used for the separation of vanillin and syringaldehyde with C18 as stationary phase and ethanol/water = 35/65 (v/v) as mobile phase at 25 degrees C. The linear model was first used to describe the isotherms of the two compounds. The Henry constants were determined by frontal analysis and the diffusion coefficient as well as mass transfer coefficient were estimated by empirical equations. Then, the triangle theory was used to design the operation conditions of the SMB system with configuration of [1, 1, 2] and followed the operation conditions were further optimized with consideration of the diffusion and mass transfer resistance. The obtained maximum feed flow rate was 0.081 mL min(-1), and the experimental purities of extract and raffinate were 97.2% and 96.9%, respectively. Finally, the constructed asynchronous SMB was used to separate vanillin and syringaldehyde with the same apparatus. The optimized average configuration was [1, 1.43, 1.57]. Through an asynchronous switching of inlet and outlet ports, the flow rate of feed was increased to 0.117 mL min-1, which is 44% higher than that of standard SMB. The experimental purities of the extract and raffinate were both higher than 97%. These results clearly demonstrate that the asynchronous 3-zone SMB can give an amiable performance and holds a high potential of wide applications.