In this work, we report on the catalytic activity of a manganese complex [(Cl)2Mn(RCOOET)], where RCOOET is ethyl-5-methyl-1-(((6-methyl-3-nitropyridin-2-yl)amino)methyl)-1H-pyrazole-3-carboxylate, in oxidation phenol or catechol by atmospheric oxygen to form o-quinone. The [(Cl)2Mn(RCOOET)] catalyzes at rate 3.74 µmol L−1 min−1 tetrahydrofuran (THF), similar manner catecholase tyrosinase.