Galactooligosaccharides syrup (GO-S) contains 38.2% of galactooligosaccharides and is widely used as a sweetening material. GO-S was studied in terms of the gassing power of Toluraspora delbrueckii and Saccharomyces cerevisiae, and the effects of adding GO-S or of replacing it on breadmaking properties were assessed. Neither type of yeast in a liquid medium resulted in fermentation when using transgalactosylated oligosaccharides, but both yeasts produced gas with the fermentative sugar in the GO-S. The addition of up to 5.0% of GO-S based on the flour weight had no effect on the gassing power of the dough when using T. delbrueckii during the second fermentation. GO-S replacement above 2.5% decreased the gassing power. The replacement or addition of GO-S had no effect on the rheological properties of non-frozen and frozen dough. In the case of S. cerevisiae, GO-S had no improving effect on the gassing power of frozen dough. In an amylographic study, GO-S had an effect on the pasting properties, the peak height being higher than that of the control with increasing concentration of GO-S. A sensory evaluation indicated an addition range from 0.5% to 2.5% of GO-S to be adequate.