Serum hepatitis B core-related antigen (HBcrAg) was shown to predict the risk of hepatocellular carcinoma (HCC) in chronic hepatitis B (CHB) patients undergoing treatment. We investigated the longitudinal profile of HBcrAg in entecavir (ETV)-treated CHB patients with subsequent HCC develop-ment. We identified HCC cases diagnosed at ≥1 year after ETV initiation. CHB patients without HCC (matched for age, sex, cirrhosis status, baseline hepatitis B virus [HBV] DNA lev-el, and ETV treatment duration) were identified as controls at an HCC:non-HCC ratio of 1:2. Serum samples were retrieved at baseline (ETV initiation) and at 3 and 5 years of ETV therapy for HBcrAg measurement (log IU/mL). In total, 180 patients (60 HCC patients matched with 120 CHB patients without HCC; median age, 56.5 years; 80.6% male; baseline HBV DNA, 5.9 log IU/mL; median follow-up, 6.8 years) were recruited. The median time from ETV initiation to HCC de-velopment was 3.2 years. HBcrAg levels were higher in HCC cases than in controls at all three time points: 5.69 log IU/ mL versus 5.02 log IU/mL (p=0.025), 4.23 log IU/mL versus 3.36 log IU/mL (p=0.007), and 3.86 log IU/mL versus 3.36 log IU/mL (p=0.009), respectively. ETV led to similar rates of decline in HBcrAg from baseline to 3 years in both groups (0.34 log IU/mL/year vs 0.39 log IU/mL/year, p=0.774), al-though the decline from 3 to 5 years was slower in the nonHCC group (0.05 log IU/mL/year) than in the HCC group (0.09log IU/mL/year, p=0.055). ETV time-dependently reduced HBcrAg in HCC and non-HCC patients. HBcrAg interpretation should consider the antiviral treatment duration.