Objective To investigate serum NK cell levels in HBeAg positive early pregnancy women with immune activation.Methods Fifty four HBeAg positive pregnant women admitted in Taizhou People's Hospital from September 2010 to April 2013 were enrolled in the study.Among them,the serum HBV DNA load decreased ≥2 log at 12 weeks after pregnancy in 24 cases (immune activation group) and HBV DNA did not decrease in 30 cases (immune tolerance group).The serum level of alanine aminotransferase (ALT),total bilirubin,HBeAg,HBV DNA load and NK cells were measured.Results At week 12 of gestation,the mean ALT levels and ALT abnormality rate in immune active group were higher than those in immune tolerance group [(146.7 ±93.1) vs.(44.1 ± 14.7) U/L,t =2.95,P＜0.05,50.0％ vs.6.7％,x2 =4.97,P ＜0.05].There was no significant difference of HBeAg level between two groups before pregnancy,while HBeAg level in immune activation group was lower than that in immune tolerance group at week 12 week of gestation [(291.8 ± 170.5) vs.(443.7 ± 289.9) S/CO,t =2.81,P ＜0.05].The percentage and absolute number of NK cells in immune activation group were higher than those in immune tolerance group [(26.7 ±9.1)％ vs.(17.1 ±7.8)％,t =2.52,P ＜0.05 and (370.9 ±136.4)/μl vs.(213.2 ±97.8)/μl,t =2.38,P ＜0.05,respectively].Conclusions In HBeAg positive early pregnant women with immune activation,the inhibition of HBV DNA might be associated with the activation of NK cells.