We have characterized the putative α-glucosidase gene (st2525) selected by total genome analysis from the acidothermophilic crenarchaeon Sulfolobus tokodaii strain 7. The ORF was cloned and expressed as a fusion protein in Escherichia coli, and recombinant ST2525 was purified by Ni-NTA affinity chromatography. Maximum activity was observed at 95°C and pH 4.0, and the enzyme exhibited stability with half-lives of 40.1 min and 7.75 min at extremely high temperatures of 100°C and 105°C, respectively. The enzyme retained at least 85% of its maximal activity in the pH range of 4.0-11.0. ST2525 exclusively hydrolyzed α-1,4-glycosidic linkages of oligosaccharides in an exo-type manner, with highest catalytic efficiency toward maltotriose. The enzyme also displayed transglycosylation activity, converting maltose to isomaltose, panose, maltotriose, isomaltotriose, etc. From these results, ST2525 could be potentially useful for starch hydrolysis as well as novel synthesis of oligosaccharides in industry.