PURPOSE: To determine the activity of α-amylase easily and r apidly, by contacting a specific water-insoluble polysaccharide complex with α-amylase, and hydrolyzing the complex to produce a water-soluble pigment oligosaccharide complex.

CONSTITUTION: A small-sized tube 1 having an inner diameter of 1W2mm is filled with (A) a powdery mixture 2 of (a) water-insoluble pigment polysaccharide complex obtained by the chemical bonding of a water-soluble reactive pigment with a polysaccharide hydrolyzable with α-amylase and (b) microcrystalline cellulose, (B) a hydrophilic water-insoluble carrier substance (e.g. diethylaminoethylated celluose) 3 and (C) glass wool 4. The tube 1 is dipped in an aqueous solution 5 containing α-amylase to effect the hydrolysis of the complex 2. The produced water-soluble pigment oligosaccharide complex is made to ascend together with the aqueous solution 5 in the tube, and adsorbed to the carrier substance 3 to effect the color development. The activity of α-amylase can be determined from the length of the colored zone.