A mimic of Cu 2 Zn 2 SOD has been investigated in detail. Its stability in solution has been obtained by the solution equilibrium study of N,N',N'',N -tetra(2-aminoethyl)-1,1,2,2,-ethanetetraamide with copper ions. The kinetics of catalytic dismutation of superoxide anions by copper(II) complex [Cu 2 (H - 4 L)] was studied using pulse radiolysis. The rate constant of catalytic dismutation of * O 2 - was determined to be k c a t = 2.81 x 10 8 (pH = 7.8) and 1.63 x 10 8 mol - 1 dm 3 s - 1 (pH = 8.3) and the mechanism of catalytic dismutation of * O 2 - was suggested. The k c a t values have been compared with those of other Cu 2 Zn 2 SOD (SOD = superoxide dismutase) mimics. The experimental results show that the novel mimic exhibits high activity and stability at about pH = 7.8.