A 1-kestose-producing strain, Scopulariopsis brevicaulis, produced two oligosaccharides, fructosylxyloside (FX) and fructosylfructosylxyloside (FFX) from sucrose and D-xylose. FX is known as an anti-cariogenic sugar, hut FFX is found to be a new sugar. FX inhibited the production of insoluble glucan, the presence of which in the mouth contributes to the development of dental caries, from sucrose by Streptococcus mutans but FFX did not. However, neither oligosaccharide was utilized as a substrate for the production of insoluble glucan. We determined the optimal culture conditions for the production of oligosaccharides to be initial sugar concentrations of 80 g/l sucrose and 80 g/l D-xylose, initial pH of 7, and incubation temperature of 30 degrees C. Under the optimal culture conditions, 50.3 g/l fructosylxyloside and 9.8 g/l fructosylfructosylxyloside were produced.