Two novel oligosaccharides, tetra-and penta-saccharides were synthesized by fructosyl transfer from 1-kestose to 4G-β-D-galactopyranosylsucrose with a purified 1F-fructosyltransferase of asparagus roots and identified as 1F-β-D-fructofuranosyl-4G-β-D-galactopyranosylsucrose, O-β-D-fructofuranosyl-(2→1)-β-D-fructofurano-syl-O-[β-D-galactopyranosyl-(1→4)]-α-D-glucopyranoside and 1F(1-β-D-fructofuranosyl)2-4G-β-D-galactopyranosylsucrose, [O-β-D-fructofuranosyl-(2→1)]2-β-D-fructofuranosyl-O-[β-D-galactopyranosyl-(1→4)]-α-D-glucopyranoside, respectively. Both oligosaccharides were scarcely hydrolyzed by carbohydrase from rat small intestine.Human intestinal bacterial growth by 1F-β-D-fructofuranosyl-4G-β-D-galactopyranosylsucrose was compared with that by the tetrasaccharides, stachyose and nystose. Bifidobacteria utilized 1F-β-D-fructofuranosyl-4G-β-D-galactopyranosylsucrose to the same extent as stachyose or nystose. On the other hand, the unfavorable bacteria, Clostridium perfringens, Escherichia coli and Enterococcus faecalis, that produce mutagenic substances did not use the synthetic oligosaccharide.