A new class of macrobicyclic dinickel(ii) complexes [Ni2L 1,2B](ClO4)4 (1-6), where L1,2 are polyaza macrobicyclic binucleating ligands, and B is a N,N-donor heterocyclic base (viz. 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen)) are synthesized and characterized. The redox, catalytic, DNA binding and DNA cleavage properties were studied. They exhibit two irreversible waves in the cathodic region around Epc = -0.95 V and Epa = -0.85 V vs. Ag/Ag+ in CH3CN-0.1 M TBAP, respectively. The first order rate constants for the hydrolysis of 4-nitrophenylphosphate to 4-nitrophenolate by the dinickel(ii) complexes 1-6 are in the range from 3.36 × 10 -5 to 10.83 × 10-5 Ms-1. The complexes 3 and 6 show good binding propensity to calf thymus DNA giving binding constant values (Kb) in the range from 3.08 × 105 to 5.37 × 105 M-1. The binding site sizes and viscosity data suggest the DNA intercalative and/or groove binding nature of the complexes. The complexes display significant hydrolytic cleavage of supercoiled pBR322DNA at pH 7.2 and 37 °C. The hydrolytic cleavage of DNA by the complexes is supported by the evidence from free radical quenching and T4 ligase ligation. The pseudo Michaelis-Menten kinetic parameters kcat = 5.44 × 10-2 h-1 and KM = 6.23 × 10-3 M for complex 3 were obtained. Complex 3 also shows an enormous enhancement of the cleavage rate, of 1.5 × 106, in comparison to the uncatalysed hydrolysis rate (k = 3.6 × 10-8 h-1) of ds-DNA. © 2012 The Royal Society of Chemistry.