Serum hepatitis B core-related antigen (HBcrAg) levels reflect intrahepatic HBV replication activity. We aimed to study whether HBcrAg levels predict response to pegylated interferon (PEG-IFN) treatment in hepatitis B e antigen (HBeAg)-positive chronic hepatitis B (CHB) patients. We studied HBcrAg levels in 222 HBeAg-positive patients treated with PEG-IFN with or without lamivudine for 52 weeks in a global randomized trial and compared kinetics across treatment arms and types of response. Optimal HBcrAg cutoffs for stopping therapy were compared to and combined with the currently recommended hepatitis B surface antigen (HBsAg)-based stopping-rules. Baseline HBcrAg levels could not discriminate between responders and non-responders (P=0.91). HBcrAg levels of patients responding to PEG-IFN therapy showed a more pronounced on-treatment decline (mean declines 3.4 versus 1.0 log U/ml; P<0.0001), which was sustained until the end of follow-up (mean declines week 78, 3.8 versus 1.0 log U/ml; P<0.0001). In the PEG-IFN monotherapy group, HBcrAg levels of >8.35 log U/ml at week 24 identified 19 patients (19%) of whom 1 (negative predicitve value [NPV]=95%) achieved a response. The performance of this HBcrAg-based stopping rule alone was not superior to the one based on HBsAg >20,000 IU/ml. Among patients with an HBsAg <20,000 (n=56), 9 (16%) had an HBcrAg >8.35, of whom 8 achieved no response (NPV 89%). HBeAg-positive CHB patients with a response to PEG-IFN therapy achieve a more pronounced HBcrAg decline. HBcrAg levels at week 24 of therapy could be used to identify non-responders in combination with the established HBsAg-based stopping-rules.