Method for determination of alpha-amylase activity

A method for determining a-amylase activity which comprises bringing a sample into contact with an a-glucosidase in the presence of an a-amylase substrate and optically determining a liberated label, the substrate being a maltooligosaccharide composed of at least 3 glucose units, whose reducing terminal glucose is bonded to an optically measurable label at the 1-position by a-glucoside linkage or b-glucoside linkage, and whose non-reducing terminal glucose is modified by a substituent other than glucose, and the a-glucosidase being substantially capable of acting on glucose to which said label is bonded at the 1-position by a-glucoside linkage and on all maltooligosaccharides having 2 to 7 glucose units; and a reagent for determining a-amylase activity comprising said a-glucosidase and said a-amylase substrate. The present invention permits, in the determination of a-amylase activity, efficient auxiliary action of adjuvant enzyme, a determination with good sensitivity, and little reagent blank reaction.