Bifidogenic effect and stimulation of short chain fatty acid (SCFA) production by fractions of oligosaccharides with a DP⩾3 and Gal β(1-6) linkages synthesised from lactose or lactulose by Pectinex Ultra SP-L and Lactozym 3000 L HP G were evaluated in human faecal slurries. Results were compared with those obtained for the commercial oligosaccharide mixture Vivinal®-GOS. Quantitative real-time PCR showed that all galacto-oligosaccharide (GOS) fractions stimulated slightly higher bifidobacteria growth than lactose, lactulose and Vivinal®-GOS. GOS fractions promoted the production of total SCFA and acetic acid in a similar way to Vivinal®-GOS and more than glucose, lactose and lactulose. In conclusion, oligosaccharides derived from lactose and lactulose may represent a suitable alternative to lactulose for the design of new functional food ingredients.