Background: There is increasing evidence that host immune responses influence antiviral efficacy in chronic hepatitis B (CHB). The aim of this study was to characterize the immunological features responsible for improved treatment responses with pegylated interferon (PEG-IFN)-alpha 2a in entecavir (ETV)-suppressed patients with CHB. Methods: Peripheral natural killer (NK) cells, Toll-like receptors (TLRs), T-cell subsets, regulatory T-cells (Tregs) and programmed death 1 (PD-1) were evaluated dynamically in 77 patients undergoing a clinical trial (OSST trial, NCT00940485) by flow cytometry. Response was defined as hepatitis B e antigen (HBeAg) seroconversion, hepatitis B surface antigen (HBsAg) loss and HBsAg seroconversion (either as singular events or in combination at week 48). Results: Compared with ETV responders or PEG-IFN-alpha non-responders, PEG-IFN-alpha responders exhibited a significant decline in HBsAg during treatment (P=0.033 and P<0.001, respectively) and a significant decline in Treg proportions from week 12 to week 24 (P=0.036 and P=0.004, respectively). Moreover, PEG-IFN-alpha responders showed a significantly higher increase in the NKG2C(+) NK cell proportions from baseline to week 12 (P=0.0073) and of TLR2(+) monocytes at week 12 than PEG-IFN-alpha non-responders (P=0.039). Conclusions: Successful response to PEG-IFN-alpha correlates with an early significant restoration of impaired immune responses. Although antiviral treatment response can be achieved by both IFN and ETV, the underlying immunological features vary which may explain the generally observed difference in off-treatment durability of response between the two treatments, as well as effects on HBsAg.