Objective To evaluate the immunogenicity of haemophilus influenza type b conjugate vaccine used in the children 3 mo through 5 years of age. Methods The healthy children 3 mo through 5 years of age from Jiangsu province were observed in this research. Infants of 3 to 5 mo-old received 3 doses of Hib-TT, infants of 6 to 11 mo-old received 2 doses, and 1 to 5 yr-old children received one dose of Hib-TT, each at an interval of one month and vastus lateralis muscle injection. Hib-PRP antibody levels in sera were determined before the first dose, 28 d after the last dose and 28 d after the booster by ELISA resp., and calculate the sera antibody GMC and GMFI. Results After the whole primary immunization series, 100% of children 3 mo through 5 years of age would achieve antibody concentrations of 1.0 μg/mL, the long-term protection. The antibody GMC in three groups of children 3 mo through 5 years of age were resp. 131.22 μg/mL, 14.86 μg/mL, 15.59 μg/mL, and the GMFI were resp. 42.13, 47.61, 121.59. After boost dose, the antibody GMC of children 3-5 mo of age was 57.21μg/mL, and 100% of children in this group achieved the antibody of long-term protection. Conclusion The Haemophilus influenza type b conjugate vaccine is proved to be efficacious in children 3 mo through 5 years of age.