ESR simulation and experimental results have been presented to show that transition metal-radical complexes can engage in intra molecular electron exchange and that the exchange gives rise to ESR asymmetric line broadening effect. Depending on the relative concentration of the redox-exchange pair, metal or radical-like spectrum can be obtained. Simulation results show that a metal-radical complex can be masked by its redox counterpart upto a relative concentration of 1:2 at a modest exchange rate of 3×10⁸/s. Asymmetric line broadening was predicted to occur upon such metal-radical complexation. Experimentally, a pronounced ESR asymmetric line broadening was observed for Cu(Ⅱ) complexes of various redox-active ligands. Cu(Ⅱ) complex with redox-inert ammonia, however, showed no such evidence. Ligand displacement experiments established the reversibility of metal-radical complexation and the associated ESR line broadening.