The correlation between electrical degradation and valence states of additives in the Bi₂O₃ and MnO₂(Bi-MnO₂) or Mn₂O₃(Bi-Mn₂O₃) added ZnO varistors and Bi₂O₃ and CoO(Bi-CoO) or Co₃O₄(Bi-Co₃O₄) added varistors was investigated by ICTS and XPS measurements. The results of ICTS and XPS measurements showed that Mn as the additive contributes differently to the factors of degradation in the cases of Bi-MnO₂ and Bi-Mn₂O₃ added ZnO and Co as the additive contributes similarly to the factors of degradation in the cases of Bi-CoO and Bi-Co₃O₄ added ZnO. The recovery of varistor characteristics of Bi-Mn-Co added ZnO added Co₃O₄ after degradation was more remarkable than that of the sample added CoO by the thermal annealing. The results of ICTS measurements showed that the interface states changed for Bi-Mn-Co added ZnO after the thermal annealing. XPS spectra of the Co-2p_3/2 orbit and Mn-2p_3/2 orbit for Bi-Mn-Co added ZnO showed different binding energies after degradation.