The present invention aims to provide a novel process for producing isomaltose and isomaltitol, and uses thereof, and it solves the object by establishing a process for producing isomaltose comprising a step of contacting a saccharide, having the .alpha.-1,4 glucosidic linkage as the linkage of non-reducing end and a glucose polymerization degree of at least two, with an .alpha.-isomaltosyl-transferring enzyme and an .alpha.-isomaltosylglucosaccharide-forming enzyme derived from a specific microorganism; a process for producing isomaltitol using the isomaltose produced by the above process; saccharide compositions comprising the isomaltose and/or the isomaltitol produced by the above processes; and uses thereof.