The aim of this study is to elucidate the important role of the previous infection of HBV, and the relations among HBV genome integration and p53 gene mutation, telomerase activity and genetic instability in liver tissue with HBsAg-negative (NB) and anti-HCV negative (NC) hepatocellular carcinoma (HCC). We examined the backgrounds of 34 NB and NC (NBNC) Japanese patients with chronic liver disease (CLD) patients not associated with HCC and 26 NBNC CLD patients with HCC. HBV genome integration into host cell genome, p53 gene mutation telomerase activity and genetic instability were examined in 6 with NBNC HCC (NBNC-HCC) tumorous tissue (T) and non-tumorous tissues (NT). In the NBNC group, HBV-related antibody positive patients with HCC are significantly more than the patients without HCC. Moreover, concerning the stage of the coexisted liver diseases, in NBNC CLD, LC patients with HCC is 19 of 26 (73.1%) , on the other hand, LC patients without HCC is 16 of 34 (47.1%). LC patients with HCC group is significantly more than that without HCC. Three (50%) of 6 in T and 3 cases (50% ) in NT were found to integrated genome of HBV. p53 gene mutation was observed in 3 (50%) of T. Concerning the telomerase activity, 3 of 6 cases (50%) in T and 1 case in NT was recognized. There was no genetic instability (LOH or RER) of D2S123, D3S1067 and TP 53 in T and NT. Finally in T of NBNC HCC cases, TTVDNA was detected in 3 of 5. Even in the HBsAg-negative and anti-HCV negative HCC cases, CLD coexisting with LC, previous HBV infection and HBVDNA integration were observed. There were a few cases with HBVDNA integration, p53 gene mutation, telomerase activity and genetic instability, simultaneously in HCC tissue, and in some cases, the coexistence with TTVDNA were concurrently confirmed. It is speculated that the important role of the previous infection of HBV may have also been proposed for HCC oncogentic progression in NBNC CLD [corrected].