The expression of phosphorylated-ATM (p-ATM) reflecting the activation of ATM, p21(WAF1/Cip1) and 8-hydroxy-deoxyguanosine (8-OHdG), an oxidative stress marker, was examined immunohistochemically in the liver tissues of 20 cases of stage 1/2 PBC, 9 extrahepatic biliary obstruction (EBO), 35 chronic viral hepatitis (CVH), 17 nonalcoholic steatohepatitis (NASH), and 18 histologically normal liver. p21(WAF1/Cip1), p-ATM and 8-OHdG were frequently and extensively co-expressed in the nuclei of CNSDC in PBC, and their expressions were correlated.