Abstract: Egg-type Hyline breeders were vaccinated with cell-adapted reticuloendotheliosis virus (REV) strain REV-C99(p30), all chickens became REV-antibody positive 2w after vaccination. And all chicks (10/10) from vaccinated breeders were REV-maternal antibody positive within 7 days after hatch. To compare preventive effects of maternal antibody on immunosuppression induced by homologous and heterologous REV, both REV-maternal antibody positive and negative chicks were inoculated with homologous strain REV-C99(p3) of low passage and heterologous REV field stain HA9901. The results indicated that REV-specific maternal antibody was able to effectively prevent immunosuppression induced by homologous or heterologous REV strains as the hemagglutinatin inhibition antibody titers were compared after vaccination with inactivated vaccines against H5 and H9 avian influenza viruses.