Objective To investigate the immunization effect of influenza A/H1N1 vaccine in health care workers (HCW) in Inner Mongolia Greater Khingan Mountains area. Methods Five hundred and five HCW who received A/H1N1 influenza vaccination (immunized group) and 129 staffs who didn't receive the vaccination (unimmunized group) were randomly sampled for semiquantitative testing of serum H1N1 antibody (IgG) levels by enzyme-linked immunosorbent assay (ELISA).Results were analyzed and stratified by age, sex, occupation and the time interval between the time of vaccination and serum sample collection. The antibody positive rates of the two groups were compared by x2test. Results There were 401 (79. 4%) HCW whose H1N1 antibody were positive and 50 (9.9%) whose antibody were weak positive among 505 immunized HCW. While among 129 unimmunized HCW, there were 59 (45.7%) whose antibody were positive and 15 (11.6%) whose antibody were weak positive. The seroconversion rates of specific antibody were not significantly different among the different age groups after receiving A/H1N1 influenza vaccine (P＞ 0.05).However, there were statistical differences of the seroconversion rates among different sex groups (men 95.7% vs women 87.4% in immunized group, x2=6.40, P＜0.05; and men 73.3% vs women 52.5% in unimmunized group, x2 =4.07, P＜0.05) and different occupation groups (doctor 86.0% vs nurse 94.5% in immunized group, x2 = 9. 16, P＜0.01; and doctor 43. 8% vs nurse 75.0% in unimmunized group, x2=12.61, P＜0.01 ). The seroconversion rate was 81.5% after 80 to 89 days of vaccination, which was significantly lower than those after 30 to 39, 50 to 59 days and 60 to 69 days of vaccination, which was 100.0%, 94.7% and 93.6%, respectively (x2 =3.96, P ＜0.05; x2=7.15, P ＜0. 01; x2 = 9. 98, P＜0. 01). Conclusions A/H1N1 influenza vaccination can induce effective immune response in HCW in Greater Khingan Mountains area of Inner Mongolia. However,the level of specific antibody significantly reduces after 80 to 89 days of vaccination.