Weissella confusa VTT E-90392 is an efficient producer of a dextran that is mainly composed of alpha-(1 -> 6)-linked D-glucosyl units and very few alpha-(1 -> 3) branch linkages. A mixture of the Chaetomium erraticum endodextranase and the Aspergillus niger a-glucosidase was used to hydrolyze W. confusa dextran to glucose and a set of enzyme-resistant isomaltooligosaccharides. Two of the oligosaccharides (tetra- and hexasaccharide) were isolated in pure form and their structures elucidated. The tetrasaccharide had a nonreducing end terminal alpha-(1 -> 3)-linked glucosyl unit (alpha-D-Glcp-(1 -> 3)-alpha-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 6)-alpha-D-Glc), whereas the hexasaccharide had an alpha-(1 -> 3)-linked isomaltosyl side group (alpha-D-Glcp-(1 -> 6)[alpha-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 3)]-alpha-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 6)-alpha-D-Glc). A mixture of two isomeric oligosaccharides was also obtained in the pentasaccharide fraction, which were identified as (alpha-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 3)-alpha-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 6)-alpha-D-Glc) and (alpha-D-Glcp-(1 -> 6)[alpha-D-Glcp-(1 -> 3)]-alpha-D-Glcp-(1 -> 6)-alpha-D-Glcp-(1 -> 6)-alpha-D-Glc). The structures of the oligosaccharides indicated that W. confusa dextran contains both terminal and elongated alpha-(1 -> 3)-branches. This is the first report evidencing the presence of elongated branches in W. confusa dextran. The H-1 and C-13 NMR spectroscopic data on the enzyme-resistant isomaltooligosaccharides with alpha-(1 -> 3)-linked glucosyl and isomaltosyl groups are published here for the first time.