In this study we aims to examine the effects of 0.5 mol% Cr2O3 addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and interface state levels of ZnO-Bi2O3-Sb2O3 (Sb/Bi=0.5, 1.0, and 2.0) systems (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. The sintering and electrical properties of Cr-doped ZBS (ZBSCr) systems were controlled by Sb/Bi ratio. Pyrochlore (Zn2Bi3Sb3O14) was decomposed more than 100℃ lowered on heating in ZBS (Sb/Bi=1.0) by Cr doping. The densification of ZBSCr (Sb/Bi=0.5) system was retarded to 800℃ by unknown Bi-rich phase produced at 700℃. Pyrochlore on cooling was reproduced in all systems. And Zn7Sb2O12 spinel (α-polymorph) and δ-Bi(2)O(3) phase were formed by Cr doping. In ZBSCr, the varistor characteristics were not improved drastically (non-linear coefficient α=7~12) and independent on microstructure according to Sb/Bi ratio. Doping of Cr2O3 to ZBS seemed to form Zn(i) (0.16 eV) and Vo (0.33 eV) as dominant defects. From IS & MS, especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one (1.1 eV) and electrically inactive intergranular one (0.95 eV) with temperature.