Synthesis, crystal structure, magnetic properities and solution chemistry of binuclear copper(II) complexes which functionally mimic the catalase enzyme have been thoroughly investigated. These complexes are formulated as [BDBPH Cu2(II,II)]ClBr (1), [BDBPH Cu2(II,II)(μ-OAC)]Br (2) and [BDBPH Cu2(II,II)(μ-Oxa)] (3) (BDBPH=3,6,9,17,20,23-hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,1,111,15] triaconta-1(28), 11,13,15 (30),25,26,-hexaene). Elemental analysis, IR and electronic spectra, indicate that these complexes have macrocyclic dinuclear structures with or without additional μ-X bridging ligands. Complex 1 crystallizes in the triclinic space group P1̄, with cell constants a=11.5717(6) Å, b=11.6699(6) Å, c=13.8053(7) Å, α=70.2510(10), β=73.7970(10), γ=65.1111(10), V=1571.09(14) Å3 and Z=2. Refinements based on 5397 reflections with I>2.0σ(I) converged with R=0.0824, Rw=0.1721. The Cu(II) ions reside at the N3 (diethylenetriamine) O2 site of pyramidal geometry and are coplanar with each other through the phenol bridge. The temperature dependence of magnetic susceptibilities of 1 has been studied, giving significant antiferromagnetic spin-exchange in each dicopper(II) unit with J=−210 cm−1, g=1.98. This result is in agreement with the phenol group bridged dicopper structure. Complex 1 was found to be the most active compound for auto-catalytically dismutes H2O2 in aqueous solution with kobs=2.0×10−2. For complex 2 the μ-OAc ligand appears to dissociate and undergoes ligand substitution with H2O. Solution chemistry indicated that in mixed-ligand complex system of BDBPH–Cu(II)-(μ-Oxa) (1:2:1), the effective Cu2(II) concentration decreased significantly compared with simple BDBPHCu2 system. The observed steady-state molecularities for complex 1 showed that the reaction rate is first order in [complex 1] and zero order in [H2O2]. No induction period was needed before vigorous evolution of dioxygen occurred. ESR and UV–Vis spectra studies support a mechanism involving a Cu(I)O2Cu(I) intermediate, which was isolated and verified by IR and element analysis. As a result, a catalytic mechanism of H2O2 dismutation by this complex system was proposed.