This study was done to investigate the impact of bismuth oxide (Bi2O3) composites on the zinc oxide (ZnO) properties for varistor applications. ZnO-Bi2O3 samples were prepared using a two-step process, precipitation, and solid-state method. Bi2O3 was added into ZnO at various concentrations (0, 0.5, 1.0 and 1.5 mol%). All samples were characterized using X-ray diffraction (XRD), Scanning electron microscope (SEM) and UV visible spectroscopy. XRD results have shown that the crystallite size of ZnO-Bi2O3 samples became smaller when Bi2O3 was added from 0.5 mol% to 1.0 mol%. However, the crystallite size of ZnO-Bi2O3 increased over 1.0 mol% of Bi2O3 concentration. The smallest particle and grain size of ZnO-Bi2O3 appeared when composite at 1.0 mol% concentration of Bi2O3. The homogeneity and smallest grain size might be suitable to be used for varistor application. The absorbance of ZnO-Bi2O3 decreased as the Bi2O3 concentration increased. Therefore, adding Bi2O3 at various concentrations into the ZnO host material can tailor its structural and optical properties.