Abstract: The aim of this study was to investigate the effect of garlic, in powder form, on serological response of broilers to NDV (Newcastle Disease Virus) vaccine. Two hundred and eighty, day-old, Ross chicks were randomly divided into groups A, B (52 each), C and D (88 each). The birds in groups A and B received control diet during the experiment, but those in groups C and D were given control diet supplemented with 1 and 3% garlic powder, respectively. After 2nd bleeding, half of the chicks in groups C and D were separated as groups E and F and fed control diet afterwards. At 9 days of age, all groups except A were inoculated with a killed NDV vaccine (Merial, France) subcutaneously and with B1 strain (Merial, France) by eye drop. Fifteen chicks were bled from each group on days 14, 24 and 34 post vaccination and also five just before vaccination. The sera were assayed for antibody against NDV by both HI and ELISA tests. The results showed that antibody titers were significantly higher in vaccinated chicks than in non-vaccinated chicks (p<0.05), but there were no significant effects of treatment on antibody level (p>0.05). Furthermore, the removal of garlic from diet had no effect on serum titer (p>0.05). It is concluded that diet supplementation with garlic powder can not enhance the serological response of broilers to NDV vaccine.