Fumonisin B1 (FB1) is a mold metabolite produced by Fusarium species that is frequently found in corn worldwide. It is toxic to both liver and kidney. This research aimed to assess the influence of grape seed extract (GSE) on reducing toxic influences of Fumonisin B1 (FB1) in broilers by examining the growth performance, immune response, antioxidant capacity and biochemical constituents. A total of 240 one-day-old Ross-308 chicks were randomly allocated into four treatments of six replicates each (10 birds per replicate), fed ad libitum for five weeks with the following dietary treatments: 1. Basal diet (control); 2. Basal diet + 400 mg/kg FB1 contaminated diet (FB1); 3. Basal diet + FB1 (400 mg/kg) + GSE (250 mg/kg); and 4. Basal diet + FB1 (400 mg/kg) + GSE (500 mg/kg). Results revealed that inclusion of FB1 in the diet of birds resulted in deleterious effects on all parameters traits included in this study. The addition of GSE at levels of 250 or 500 mg/kg of diet to the FB1–containing diet significantly improved the adverse effects of FB1 on growth performance, serum immunoglobulin contents, serum biochemical contents, and enzyme activities in the liver, malondialdehyde content and total antioxidant capacity and glutathione peroxidase concentration within the liver and serum. Moreover, 500 mg GSE / kg of diet surpasses the other level 250 mg GSE /kg diet concerning all above–mentioned the parameters. In conclusion, broilers performance,  some blood constituents, oxidative stress and liver function were significantly affected by FB1 (400 mg) treatment; the addition of GSE (250 or 500 mg/kg of diet ) to the FB1–contaminated diet significantly recovered the adverse effects of FB1 on these traits; the protective effect of 500 mg GSE /kg of diet against the toxic effects of FB1 was greater than that of 250 mg GSE/kg of diet; and these improvements may contribute to a solution of FB1 problems in broiler chickens.