We evaluated tetanus specific IgG, IgM, IgG subclasses after DPT vaccination in infants and children. Tetanus toxoid specific IgG, IgM IgG subclasses were measured to characterize the isotope profile of antibody against tetanus toxoid. The values of the tetanus specific IgG in the positive group were significantly increased compared to those of the control group, and were significantly increased after two inoculation. Tetanus specific IgG was very low in adults and neonates. In our tetanus specific IgG subclasses study, forty-five of 56 cases (80%) showed predominantly IgG1 antibody responses to tetanus toxoid, while twenty-five of 56 cases (45%) showed IgG4 responses. Both IgG1 and IgG4 responses were demonstrated in 17 cases (30%). So we suggest that IgG was mainly involved in humoral immune response after DPT vaccination, and IgG1 may play an important role among IgG subclasses. IgG4, alone or together with IgG1, can also play a role in immune response to tetanus toxoid.