It is intended to provide a novel process for producing isomaltose and usethereof. Namely, a process for producing isomaltose characterized bycomprising treating a saccharide having .alpha.-1,4-glucosyl bond as thebinding manner at the non-reducing end and having a degree of glucosepolymerization of 2 or more with a-isomaltosyl glucosaccharide synthase in theabsence or presence of a-isomaltosyl transferase to thereby synthesize .alpha.-isomaltosyl glucosacharide having .alpha.-1,6-glucosyl bond as the bindingmanner at the non-reducing end and .alpha.-1,4-glucosyl bond as the bindingmanner other than at the non-reducing end and having a degree of glucosepolymerization of 3 or more and/or cyclo{.fwdarw.6)-.alpha.-D-glucopyranosyl-(1.fwdarw.3)-.alpha.-D-glucopyranosyl-(1.fwdarw.6)-.alpha.-D-glucopyranosyl-(1.fwdarw.3)-.alpha.-D-glucopyranosyl-(1.fwdarw.}, then treating theproduct(s) with isomaltose-releasing enzyme, and collecting the thus formedisomaltose.
