The crystal structure and catecholase-like activity of a mononuclear complex, Cu(EDTB)(NO3)2.C2H5OH (here EDTB stands N,N,N',N'-tetrakis(2'-benzimidazolyl methyl)-1,2-ethanediamine) has been studied in comparison with a binuclear complex Cu2(EDTB)(NO3)4.3H2O. The results show that the reactive rate constants increase with increases of reaction temperature and pH value of intermediate. Electrospray ionization mass spectrum (ESI-MS) shows that tautomerism isomers of catechol with the title complex exist in reaction solution, and catechol is oxidized to quinone, then it is further oxidized resulting in muconic acid and its derivatives via an intradiol mechanism, just like that catalyzed by a mononuclear non-heme iron-containing dioxygenase.