PURPOSE: To obtain a stabilizing preservative of catechol capable of enhancing not only the storage atability of a catechol-containing sample in clinical examination but also measuring reliability.

CONSTITUTION: A catechol stabilizing preservative is obtained using at least one compound selected from a group consisting of a cyclic nitrogen-containing compound, a partially oxidized substance thereof and a substituted substance of the compound represented by formula CxH2x+yNy...I (wherein x is an integer of 6-24 and y is an integer of 3-8) or a covalent bond substance of the compound and crown ether represented by formula (-CH2-CH2-O-)z...II (wherein z is an integer of 2-6).