The synergistic effects of two contaminating mycotoxins aflatoxin (AF) and T-2 toxin (T-2) in the feed of poultry on the performance of broiler chickens were studied individually and in combination, by using one hundred and sixty eight day-old commercial broiler chicks obtained from a commercial hatchery and randomly separated into four groups in 2X2 Complete Randomized Design of three replicates and fourteen chicks per replicate, with dietary treatments of 0.0 (control), 0.5μg/g AF, 2.0μg/g T-2 and their combination (0.5 μg/g AF+2.0 μg/g T-2). The chicks were housed in deep litter independent conventional system with feed and water ad libitum throughout the experimental study. The toxin treated birds exhibited a significant (P#0.05) decrease in total serum protein, albumin and uric acid. The serum alanine amino transferase (ALT) levels were decreased and antibody titers against Newcastle disease (ND) and Infectious Bursal Disease (IBD) were also decreased significantly (P#0.05). These findings were more severe in the combined group of AF and T-2. Results indicated that the presence of AF and T-2 in the diet may have a very severe synergistic effect on these measured factors of the commercial chicks.