Levamisole as an immunomodulator drug has been demonstrated to improve the immune response to hepatitis B virus vaccination in haemodialysis patients. The aim of this randomized double-blind placebo-controlled trial was to evaluate the effect of levamisole supplementation on tetanus-diphtheria (Td) vaccine response rates in haemodialysis patients. Forty haemodialysis patients who had not received tetanus vaccination in a year before investigation and had unprotective anti-tetanus immunoglobulin G (IgG) levels (<0.1 international unit/mL) were enrolled and randomized into two equal groups to receive one dose of intramuscular Td vaccine supplemented with either levamisole (100 mg) or placebo daily, for 6 days before and 6 days after vaccination. The anti-tetanus IgG levels were measured 1 and 6 months after vaccination. One month post-vaccination, four patients were excluded from the levamisole group and two from the placebo group because of either death or renal transplantation. At 1 month, 13 out of 16 (81%) patients in the levamisole group as compared with six out of 18 (33%) patients in the placebo group developed protective anti-tetanus IgG levels (relative risk = 2.44, 95% confidence interval (CI) = 1.21, 4.88). From 1 to 6 months post-vaccination, one more patient in the levamisole group and two more patients in the placebo group were excluded because of renal transplantation. At 6 months, 11 out of 15 (73%) patients in the levamisole group as compared with four out of 16 (25%) patients in the placebo group still had protective anti-tetanus IgG levels (relative risk = 2.93, 95% CI = 1.19, 7.23). Supplementation of Td vaccination with levamisole may enhance seroconversion against tetanus in haemodialysis patients.