Severe acute exacerbation or liver failure induced by standard interferon-α(IFN-α) therapy had been reported to occur in few patients with chronic hepatitis B. However, no report showed that pegylated interferon-α therapy was able to induce severe acute exacerbation of chronic hepatitis B. Here, we describe three patients with severe acute exacerbation of chronic hepatitis B during pegylated interferon-α2a (Pegasys) treatment. One patient progressed into acute-on-chronic liver failure (ACLF) at the second week of Pegasys treatment. Two patients progressed into acute-on-chronic pre-liver failure (pre-ACLF) at the second and eighth week of Pegasys treatment, respectively. Three patients recovered after early combined intervention with corticosteroid and lamivudine. Our data indicated that there was a risk of severe acute exacerbation among patients with chronic hepatitis B during receiving Pegasys treatment. Importantly, early combined intervention with corticosteroid and lamivudine should be introduced to prevent the disease progression and improve their prognosis once severe acute exacerbation was diagnosed.