Cyclomaltodextrin glucanotransferase from Bacillus stearothermophilus produced a series of glycosyl-trehaloses through the transglycosylation reaction with cyclomaltohexaose as the glycosyl donor and trehalose as its acceptor. After beta-amylase treatment, five species of glycosyl-trehaloses were isolated by column chromatography. After chemical and enzymatic analyses, it was concluded that these oligosaccharides were alpha-maltosyl alpha-D-glucopyranoside, alpha-maltotriosyl alpha-D-glucopyranoside, alpha-maltosyl alpha-maltoside, alpha-maltotriosyl alpha-maltoside, and alpha-maltotriosyl alpha-maltotrioside. These were not hydrolyzed by salivary amylase, artificial gastric juice, or pancreatic amylase, however they were hydrolyzed by enzymes of the small intestine.