To observe longitudinally the expression of Programmed death 1(PD-1) on peripheral blood T cells in chronic hepatitis B patients underwent antiviral treatment with entecavir (ETV) and to explore the relationship between PD-1 expression and HBeAg seroconversion. Twenty HBeAg positive patients underwent antiviral treatment with ETV were followed up for 51 weeks. 14 patients remained HBeAg positive and 6 patients achieved HBeAg seroconversion. Peripheral blood was collected at six time points: T0: baseline, T1: 2-4week; T2: 5-10week; T3: 11-20week; T4: 21-30week: T5: 31-51week. PD-1 expressions on T cells were assessed by flow cytometry. Serum HBV DNA loads were determined by real-time fluorescent quantitative polymerase chain reaction (PCR) and serum ALT levels were examined at the same time. At baseline, serum HBV DNA load of patients without HBeAg seroconversion and with HBeAg seroconversion were (7.54+/-0.67) log10 copies/ml and (7.30+/-0.79) log10 copies/ml (P more than 0.05), the ALT levels were (187.26+/-184.15) U/L and (272.17+/-215.07) U/L (P more than 0.05), PD-1 exprissions on CD4+ T cells were 6.04%+/-3.71% and 6.77%+/-2.88% (P more than 0.05), PD-1 exprissions on CD8+ T cells were 6.39%+/-3.33% and 8.88%+/-2.84% (P more than 0.05). After ETV treatment, serum HBV DNA loads and ALT levels both decreased gradually, which was positively correlated with PD-1 expressions on CD4+ and CD8+ T cells (r=0.212, P = 0.05; r=0.377, P less than 0.01; r=0.279, P less than 0.05; r=0.347, P less than 0.01). During the same monitoring period, the HBV DNA loads, ALT levels and PD-1 expressions on T cells of the patients with HBeAg seroconversion decreased significantly as compared with the patients without HBeAg seroconversion. Besides, the decrease of HBV DNA loads during period deltaT0-T1 and deltaT0-T2 and PD-1 expressions on CD8+ T cells during period deltaT0-T2 and deltaT0-T3 were significantly different between these two kinds of patients (49.9% vs 37.3%, P less than 0.05; 56.7% vs 47.4%, P less than 0.05; 70.1% vs -4.2%, P less than 0.05; 66.9% vs 24.5%, P less than 0.05). The rapid decrease of PD-1 expression on peripheral CD8+ T cells after antiviral treatment with ETV is positvely correlated with the decrease of serum HBV DNA loads and may be used as a predictive index for HBeAg seroconversion in HBeAg positive patients.