This study was applied on two broiler flocks. Chickens in the experiment were divided into two groups, the first group was generated from unvaccinated breeders, while the second one was generated from breeders which was vaccinated with attenuated live vaccine of CIA. Indirect ELISA test was applied in this study to observe the maternal immunity levels and its decrease in both groups. The results showed that the maternal immunity levels in the second group was higher than the levels in the first one. The CV% which expresses the homogeneity of flock immunity levels was compared. It was found that the homogeneity in the second group was higher than that of the first one. The decrease rate of maternal immunity levels of CIA was compared in both groups. The results showed that it was higher in the first group. The results of this experiment showed the necessity of vaccination in breeders against CIA to produce good protected chicken with protective immunity levels.