This experiment was conducted to investigate the immuno-modulatory activity of aqueous leaf extract of Moringa oleifera on immune response of broiler chickens to Newcastle disease (ND) vaccinations. The performance, blood parameters and serum biochemistry of the birds were also determined. A total of one hundred and twenty (120) day-old commercial broiler chicks were randomly allotted to 3 dietary treatments of 4 replicates each. Each replicate had 10 birds. The treatments: T1 – Control group in which the birds were not given any extract; T2 and T3 – birds in these groups were given the prepared stock solution of Moringa oleifera leaf extract at dose rate of 2500mg/kg and 5000mg/kg of body weight in drinking water. The experimental birds were vaccinated with ND vaccines using a stipulated vaccination regime. The Moringa oleifera leaf extract exhibited significant (p≤0.05) influence on final body weight of the experimental broiler chickens with birds in T3 having an average weight of 1947.43g and birds in T1had 1733.33g. The immune modulating effect of the leaf extract was insignificant (p≥0.05) though it elicited higher antibody titre of Log27 and Log29 in birds in T3 compared to Log26 and Log28 of birds in control group after the first and second ND vaccinations respectively. The leaf extract caused significant (p≤0.05) increase in white blood cells and leucocytes count. The study concluded that the plant extract had slight immune stimulatory effects on response to ND vaccinations and improved the growth performance of broiler chickens.