A trial was carried out to shed more light on the precautionary efficiency of Lactobacillus acidophilus and Saccharomyces cerevisiae in ameliorating the toxic effects of aflatoxin B1 (AFB1) in broiler chicks. Two hundred and forty one-day-old unsexed Cobb broilers chicks were separated randomly into four equal experimental groups; with three replicates of 20 chicks each. The first group was received basal diet without aflatoxin B1 (control negative), while the other three groups were given basal diets containing 300 ppb AFB1. Within each aflatoxin treatment, the first group (control positive) was fed the contaminated diet without any treatment; the second was fed contaminated diet treated with L. acidophilus and the third was fed contaminated diet treated with S. cerevisiae. At the end of the experiment, biochemical traits, HI titer, and histopathological profile of broilers fed contaminated diet (300ppb AFB1/kg) (treated and not treated) were studied. The results showed that serum total protein, albumin, globulin, IgG and Ig, cholesterol and triglycerides were significantly decreased in the broilers fed diet containing 300 Ppb AFB1 as compared with those fed negative control diet. However, the activity of ALT and AST in blood serum was significantly increased in the broilers fed diet containing 300 Ppb AFB1 as compared with negative control. The same trend was observed in concentration of uric acid and creatinine. Although, all groups had haemaglutination inhibiting antibodies against NDV, the highest haemaglutination inhibiting antibody titer was obtained from birds not exposed to AFB1 at 35 days of age. In addition, data showed that the biological treatment by L. acidophilus or S. cerevisiae did not influence the humoral immune response of broiler against NDV. In addition, the histopathological study showed the ability of biological treatment to reduce the negative effects of AFB1 on liver and kidney tissues. It could be recommended that using L. acidophilus and S. cerevisiae supplementation in the feed to ameliorate toxic effects of aflatoxin B1 in broilers.