Six cerium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-one thiosemicarbazones have been prepared and characterized by elemental analyses, molecular weight determinations, molar conductance, IR, magnetic, cyclic voltammetric and thermal studies. Generally, cerium(III) may be easily converted to cerium(IV). In order to ascertain the oxidation state of the cerium in the prepared complexes, the cyclic voltammetric studies have been carried out. It has been observed that increase of potential produces an anodic peak in both the complexes. This indicates that the complexes are getting oxidized which consequently means that they were in the reduced form initially. Thus it is confirmed that cerium is present in +3 oxidation state in its complexes. This is further supported by the studies on concentration effect and sweep rate. Based on the above observations, 10-coordinated structure has been proposed for the complexes.