AbstractSugar beet molasses vinasse is a by‐product of ethanol fermentation from sugar beet molasses. Its dark brown colour, which is attributable to the presence of caramels, melanoidins and invert alkaline degradation products, cannot be removed by biological methods. The novelty of this work lies in the use of conventional strongly alkaline ion‐exchange resins for the decolourisation of sugar beet molasses vinasse. The aim of the study was to determine the efficiency of two strong‐base ion‐exchange resins, Dowex 2 and Wofatit ES, when used for the decolourisation of sugar beet molasses vinasse. Optimal conditions and extent of decolourisation were related to the concentration and pH of the vinasse, the time of reaction with the resin, and also to the dose and type of the resin used. The greatest extent of decolourisation (92%) was achieved with Wofatit ES dosed in the amount of 5 g/100 mL of 25% vinasse with an initial pH of 10. The optimal time of reaction with the resin indispensable for attaining the maximal effect of decolourisation was 1.5 h for both resins. The highest extent of reduction in chemical oxygen demand (43%) during decolourisation of 25% vinasse (pH 10) was obtained with Dowex 2.