Isomalto-oligosaccharides were produced using Leuconostoc mesenteroides B-512 FM dextransucrase immobilized in alginate fibres. Immobilization resulted in 90% relative activity. The immobilized enzyme retained activity for ten batch reactions without a decrease in activity and was reacted with a substrate composed of sucrose (1 M) and glucose (1 M) to obtain isomalto-oligosaccharides. Immobilization of dextransucrase in alginate fibre is superior to that in alginate beads in terms of immobilization yield and repetitive use. (C) 2002 Elsevier Science Ltd. All rights reserved.