Iron(III) and nickel(II) complexes from acetylacetone-S-methyl-thiosemicarbazone were synthesized and characterized. The thiosemicarbazidato structures of N2O2 are N-1-acetylacetone, N-4-salicyl/3-methoxy/5-bromo-/3,5-dichlorosalicylidene. The square-pyramidal iron(III) and square-planar nickel(II) complexes of N-1-acetylacetone-N-4-3-methoxy thiosemicarbazidato were determined by X-ray diffraction. Electrochemical characterizations of the complexes were carried out by using cyclic voltammetry and square wave voltammetry. While nickel(II) complexes only give ligand based reduction and oxidation reactions, iron(III) complexes give reversible Fe-III/Fe-II reduction in addition to the ligand based processes. Changing of the substituents on the ligand, shifts the redox processes and also affects the stabilities of the electrogenerated species. With respect to the reduction potential of Fe-III/Fe-II couple, the most easily reduced complex was 3,5-dichloro substituted complexes and the most difficult to reduce was the 3-methoxy substituted one.