We have investigated the effect of CoQ10 to lipid peroxide (LPO) and Cu, Zn-SOD in the regenerating liver in rats. Cu, Zn-SOD was investigated in biochemical activity, and immunohistochemical localization. In normal control liver, Cu, Zn-SOD was diffusely stained throughout the hepatic lobules, with predominance in the centrilobular area and with vicinity of thick portal vein. In early stage of regenerating liver. LPO was increased and Cu, Zu-SOD was decreased. Destruction of the membrane of hepatocyte was confirmed by electron microscopy in the early stage of regenerating liver, Cu, Zn-SOD might be speculated to leak out into extra cellular spaces. CoQ10 suppressed the mentioned phenomenon in regenerating liver.