An object of the present invention is to provide a means for the measurement of amylase activity that exists in a biological sample such as saliva in a more convenient manner and particularly to provide a means (method and reagent) where a sample containing amylase in high concentration is directly measured without dilution. In the present invention, there has been found a method, which is an enzymatic method using a modified oligosaccharide substrate, comprising adding saccharide such as oligosaccharide that is competitive to the oligosaccharide substrate whereupon amylase activity in an amylase sample having a high activity value can be directly measured without dilution, and a result, the present invention has been achieved.