We have succeeded in synthesizing the NiIII complexes doped by CoIII ions, [Ni1-xCox(chxn)2Br]Br2 (x = 0, 0.043, 0.093, and 0.118) by using an electrochemical oxidation method. The single-crystal reflectance spectrum of x = 0.118 shows an intense CT band about 0.5 eV, which is lower than that of [Ni(chxn)2Br]Br2 (1.3 eV). The single-crystal electrical conductivities at room temperature of these compounds increase with increase of the amounts of doping of CoIII ions. In the ESR spectra, peak-to-peak line widths ΔHpp at room temperature change about 600 G in [Ni(chxn)2Br]-Br2 to 200 G in x = 0.118. Such a large x dependence of ΔHpp seems to be ascribed to the increasing contribution from the increasing Curie spins which have smaller line width. Therefore, we have tuned the electronic structures of quasi-one-dimensional bromo-bridged NiIII complexes with strong electron correlations by doping of CoIII ions.