PURPOSE: To determine α-amylase activity accurately even in the presence of glucose in the specimen, by using a substrate consisting of a mal-tooligosaccharide having p-aminophenyl group bonded to the reducible terminal, reacting the substrate with a specimen containing α-amylase and determining the isolated p-aminophenol.

CONSTITUTION: A maltooligosaccharide having p-aminophenyl group bonded to the reducible terminal (preferably maltotetraose, maltopentaose, maltohexaose or maltoheptaose) is used as the substrate, and is made to react with a specimen containing α-amylase. The isolated p-aminophenol is coupled with a coupler such as phenol in the presence of an oxidizing agent and the produced indophenol dye is determined by conventional method such as colorimetry to determine the α-amylase activity of the specimen.