A mixture of galacto-oligosaccharides and non-prebiotic sugars was separated using a simulated moving bed unit equipped with eight packed-bed columns of a cation exchanger. In order to determine operating conditions using triangle theory, equilibrium adsorption isotherms of galactose, glucose, lactose, tri- and tetragalacto-oligosaccharide were measured. It was found that each column of the SMB unit had a maximum separation efficiency of more than 3000 theoretical plates. The achieved purity of galacto-oligosaccharides in the raffinate stream was 99.9 %, similarly 99.9 % of extract was formed by non-prebiotic sugars lactose, glucose and galactose. The productivities in the raffinate and extract, were 0.6 g/(L h) and 2.4 g/(L h), respectively.