Abstract: The synthesis of four types of Co (Ⅱ) meso-nitrooctaethylporphyrins are described; the data of their electronic absorption spectra, half wave potentials of redox and equillibrium constants of axial coordination with several ligands are reported. The more meso-nitro grouos the porphyrin has, the stronger the coordinating ability of the central cobalt ion achieves except with Ps, which shows some steric effect. The half wave potentials of both oxidation and reduction are increased by electron withdrawing nitro groups. The cyclic voltammograms of these porphyrins show quasi reversible processes for oxidation and first ring reduction, only the latter being a two electron process.