AIM: To detect the DNA binding activity of nuclear investigate the effects of NF-KB on rat hepatocyte regeneration and apoptosis after 70% portal branch ligation.METHODS: Sixty Wistar rats were randomly divided into control group and portal branch ligation group.The animals were killed 12 h, 1, 2, 3, 7, and 14 d after surgery to determine the contents of plasma ALT.Hepatocytes were isolated and nuclear protein was extracted. DNA binding activity of NF-KB was measured by EMSA. Hepatocyte regeneration and apoptosis were observed under microscope by TUNEL staining. The ultrastructural changes of liver were observed under electron microscope.RESULTS: Seventy percent portal branch ligation produced atrophy of the ligated lobes and the perfused lobes underwent compensatory regeneration, the total liver weight and plasma ALT levels were maintained at the level of sham-operated animals throughout the experiment. After 2 d of portal branch ligation, DNA reached its peak, the number of apoptotic hepatocyte in the ligated lobes and the number of mitotic hepatocyte in the perfused lobes also reached their peak. Typical apoptotic changes and evident fibrotic changes in the ligated lobes were observed under electron microscope.CONCLUSION: After 70% portal branch ligation, DNA binding activity of NF-KB in hepatocyte is significantly increased and NF-KB plays an important role in hepatocyte regeneration and apoptosis.