The aim of the study was to investigate the toxic effects of aflatoxin B₁ (AFB₁) and efficacy of a probiotic preparation containing L. reuteri, L. plantarum, L. pentosus, L. rhamnosus and L. paracasei and Saccharomyces cerevisiae yeasts to ameliorate their effects in broiler chickens. A total of 168 one-day-old female Ross 308 broilers were randomly allocated to six groups. Three wheat and soybean meal-based diets were prepared: Control diet and diets contaminated with 1 or 5 mg/kg AFB₁ supplied in moldy wheat. All diets were unsupplemented or supplemented with probiotic, cold pelleted and fed from 1 to 35 day of life. Feeding diet with 1 mg AFB₁/kg did not affect performance, but a diet with 5 mg AFB₁ resulted in a significant reduction of feed intake and BWG, both diets induced liver and kidneys enlargement. The probiotic supplementation of the diets partially ameliorated those negative effects and resulted in a significant increase of AFB₁ excretion. It was accompanied by the reduced level of AFB₁ residues in the liver from 8.9 to 3.7 and from 11.8 to 5.9 µg/kg, in kidneys from 7.9 to 2.5 and from 13.7 to 4.1 µg/kg in birds fed the less and more contaminated diets, respectively. AFB₁ exposure caused many severe histopathological changes in the liver and kidneys of broilers, probiotic supplementation significantly reduced the changes of these organs. It may be concluded that the probiotic supplementation can be used to alleviate the negative effects of contamination of broiler feed with AFB₁ on bird health and product security.