It has already been reported that α-amylase from Streptomyces hygroscopicus SF-1084 and Streptomyces praecox NA-273 hydrolyze starch to produce more than 75% maltose which rather higher than that produced by other α-amylases. There are two possible mechanisms for higher amount of maltose accumulation than would result from direct hydrolysis of maltotriose; one is condensation and the other is transglycosylation. To make clear the mechanism of higher amount of maltose accumulation, we studied the further conversion of maltotriose using cold and labelled maltotriose. The experiment showed the molar ratio of maltose was higher than glucose. From the results of our studies, it was seen that transglycosylation followed by hydrolysis played an important part in maltose accumulation.