Objective To investigate the effect of Low molecular weight heparin sodium (LMWH-Na) adjuvant on humoral immune response induced by hepatitis A virus(HAV)vaccine in mice. Methods ICR mice were randomly divided into 8 groups, six for each, and the mouse of each group are injected respectively with live attenuated hepatitis A vaccine HepA-1(18 EU) +different doses (100 μL, 20 μL, 10 μL, 1 μL, 0.1 μL) of LMWH-Na, while those injected with physiological saline as a negative control group (Blank), those injected with HepA- 1(18 EU) as positive control group, those injected with Al(OH)₃(300 μg)+HepA-1(18 EU) as the aluminium adjuvant control group, 200μL for each. The specific IgG level against HAV in sera of mice at weeks 4, 8, 12 and 16 after immunization were determined by indirect ELISA. During the experiment, the health status of the mice were observed, the kidney, spleen, liver, lung and heart of mice immunized with LMWH-Na 100 μL at the maximum dosage and those in negative control group were taken out at week 16 after immunization, and prepared into sections for pathological observation. Results In addition to the negative control group, mice in various group produced anti -HAV IgG at 4 weeks after the immunization, of which the levels increased as time went on, and reached peak values at week 8 then decreased gradually. At 4 week and 8 week, the anti -HAV IgG levels of aluminum adjuvant control group, LMWH-Na 100 μL group, LMWH-Na 20μL group, LMWH-Na 10 μL group were higher than the positive control group and the difference was statistically significant (P < 0.05). At 12 week, the anti -HAV IgG levels of aluminum adjuvant control group, LMWH-Na 20 μL group and LMWH-Na 10 μL group were higher than the positive control group and the difference was statistically significant (P < 0.05). 16 week,the anti -HAV IgG levels of aluminum adjuvant control group and LMWH-Na 10 μL group were higher than positive control group and the difference was statistically significant (P < 0.05),but the anti-HAV IgG levels of various LMWH-Na groups were lower than the aluminum adjuvant control group. Conclusions LMWH-Na can obviously enhance the HAV antigen induced humoral immune response in mice,and have a value of becoming a new type of vaccine adjuvant.