Abstract: The persistence of passively administered antibodies (Abs) in the chicken sera and their role in the protection against Newcastle disease virus (NDV) challenge were determined in this study. Haemagglutination inhibition (HI) test was employed to measure the Ab titres in chicks sera. Clinical signs were observed and moralities were recorded, after challenge with the virulent virus, to determine the protection levels offered. High levels of Abs were detected in sera of chicks received single dose of yolk extracts (YE), derived from immune chickens, and remained for more than seven weeks after injection. Much higher levels of Abs were detected in sera of chicks received booster dose of the YE as compared to that received single dose. Following challenge, 90% and total protection were obtained in chicks received single and booster dose of the YE respectively.