Objective To study the relationship between serum HBV DNA level and apoptosis of peripheral blood mononuclear cells (PBMC) , and the relationship between serum HBV DNA level and the activity of caspase-8 in the patients with chronic hepatitis B (CHB). Method 30 CHB patients were selected as experimental group, and it was divided into three subgroups according to the serum HBV DNA level, subgroup A (high serum HBVDNA), subgroup B (medium serum HBVDNA), and subgroup C (low serum HBVDNA). 10 healthy adults were random selected as control group. PBMC were isolated from two groups by separating medium of lymphocytic cell and culturing it with phytohemagglutinin (PHA) in vitro for 72 hours. The PBMC was stained with PI and the apoptosis was assayed with flow cytometry. At the same time, the aetivity of caspase-8 of PBMC was assayed by color matching. Results The apoptosis rate of PBMC of experimental group ( 26. 88 ± 7.37 ) % were higher than that of the control group ( 14. 95 ±2. 53)% ( P <0. 01 ). In the experimental group, the apoptosis rate of PBMC of subgroups A, B and C showed decreasing order (34. 75 ± 4. 59)%, (25.63 ± 3.55 )%, ( 18. 91 ± 3. 81 )%. The activity of caspase-8 of experimental group 2. 99 ±0. 82 were higher than that of the control group 1.43 ±0. 91 ( P <0. 01 ). The activity of caspase-8 of subgroup A, B and C showed the same decreasing order: 3. 87 ±0. 35,2. 95 ± 0. 36, 1.95 ± 0. 29. There was a positive correlation between the apoptosis level of PBMC and the activity of caspase-8 in experimen tal group ( r = 0. 610, P < 0. 01 ). Conclusion AICD of PBMC was found in patients with CHB. The activity of caspase-8 increased in that process, and it may participate in the transduction of apoptosis signal. Serum HBV DNA level was related with the apoptosis rate of PBMC and the activity of caspase-8, and it may be one of the reasons of apoptosis in PBMC.