Galactotriose (G3), which is contained in a crude galacto-oligosaccharides (GOS) mixture coming from enzymatic transgalactosylation reactions, is known to have potential as a high-grade prebiotic ingredient. This has aroused an interest in the high-purity recovery of G3 from a crude GOS mixture, which included monosaccharides (galactose and glucose), disaccharides (G2), and GOS components with different degrees of polymerization (G3, G4, and G5). To settle this problem, we aimed to develop an efficient simulated-moving-bed (SMB) process for high-purity recovery of G3 from the crude GOS mixture. It was found first that the appropriate column temperature and ionic form of the adopted adsorbent in consideration of both G3-G2 and G3-G4 resolutions were 65 °C and K+ form respectively. Under such adsorbent conditions, the equilibrium constants and mass-transfer parameters of the crude mixture components were determined and then exploited in the design of the G3-recovery SMB, which was carried out with a priority focus on the stable maintenance of high purity for G3 product throughout the SMB operation. The separation performance of such designed SMB was verified on the bases of the column profiles from simulations and the outlet-concentration data from the relevant SMB experiment. Overall, it was confirmed that the designed SMB could recover G3 from the crude GOS mixture in a continuous mode with a purity of more than 98.9% while keeping the overall loss of G3 below 7.3%.