AbstractSilver nanoparticles (AgNPs) are a powerful disinfectant, but little information is available on their potential use as a growth promoter and the safety margin of this. In this study, 480 1-day-old Cobb chicks were assigned to one control and three treated groups. The treated groups were supplemented with silver-doped silica nanoparticles (SiO₂@AgNPs) at three dietary levels (8, 16, and 20 mg/kg diet) for 35 days. The results revealed no significant changes in the growth performance and oxidative parameters, and in most of the hematological and biochemical parameters among the control and treated groups. In contrast, dose-dependent adverse effects were exerted on the histopathological structure and immunohistochemical expression of CD45 in liver, kidneys, and lymphoid organs (spleen, bursa, and thymus). In addition, the relative weight of lymphoid organs and the serum levels of immunoglobulins M and G were significantly diminished. Moreover, the gene expression of proinflammatory cytokines (IL-β1 and TNF-α) and the ultrastructural morphology in breast muscle showed significant dose-dependent alterations. It could be concluded that the dietary supplementation of SiO₂@AgNPs at a level of 8 mg/kg diet or more has dose-dependent proinflammatory and immunosuppressive effects on broiler chickens.