Abstract: Immunological effect of combined inoculation of the inactivated vaccines for Newcastleand the infectious bursal diseases (ND-IBD) on egg-laying chickens was investigated. For the study, 360 one-day-old commercial chicks were randomly divided into 3 groups. The chicks in one group were immunized immediately with the two vaccines simultaneously, another when they were 7-day-old, and the third group injected with saline solution as control.Levels of ND-IBD antibodies in the serum ofthese chicks were determined, spleen biopsies for disease detection executed, and qPCR on mRNA expressions of CD4⁺, CD8⁺, IL-6 and IFN-β performed every 7 days during the period of 21 to 56 d. The results showed that all treated one-or 7-day-old birds had higher antibody levels than control, and could fence off IBD virus infection. The 7-day-old group showed greater immunity against the diseases, and significantly increased mRNA expressions on CD4⁺, CD8⁺, IL-6 and IFN-β over control. It was, therefore, concluded that, by combining vaccinations against ND-IBD on 7-day-old egg-laying chicks, a desirable immunological effect on the chickens could be achieved.