PURPOSE: To obtain the titled analytical element, containing a substrate which is phosphoric acid esters of a self-nondeveloping compound capable of bimolecularly condensing in the presence of an oxidizing agent by action of an enzyme to form a coloring matter and a specific buffer agent in separate and different layers and having excellent sensitivity as well as preservation stability.

CONSTITUTION: A reagent layer containing a buffer agent having ≥8.0pKa value, e.g. 2-ethylaminoethanol, etc., is provided on a transparent support, e.g. polyethylene terephthalate, etc., and a porous developing layer containing a compound which is a phosphoric acid ester of a self-nondeveloping compound or a salt thereof, e.g. 5-bromo-4-chloro-3-indolyl phosphate toluidine salt, etc., and capable of bimolecularly condensing the nondeveloping compound formed in the presence of an oxidizing agent by action of the alkaline phosphatase in a liquid sample to form a coloring matter as a substrate for measuring alkaline phosphatase activity is provided thereon. Thereby the aimed analytical element having the substrate and buffer agent mutually present in the separate and different layers is obtained.