A study on the effect of the modify values of x in CaCu3-xMn4+xO12 system has been carried out with x = 0.1, 0.3, 0.5, 0.7 and 0.9. The materials were prepared via solid-state reaction. The preparation conditions have been optimized using thermogravimetry analysis (TGA) technique. Material formations under the reported conditions have been confirmed by X-ray diffraction (XRD) studies. The results show that the formation of CaCu3Mn4O12 started at calcinations temperature of 600 0 C with the presence of raw material and was formed completely at 850 0 C. Field emission scanning electron microscopy (FESEM) analysis indicated that the increase of x value in the composition had changed the microstructures to be more faceted. The impedance spectrum is characterized by the appearance of two semicircle arcs whose pattern of evolution changes with rise of values x in the CaCu3-xMn4+xMn4O12 system. Bulk resistance (Rb) and grain boundary resistance (Rgb) of CaCu3- xMn4+xO12 decreases form 824.24 : to 98.68 : and 418.18 : to 2.20 : respectively, with the increasing of x value.