The aim of the present study was to assess the genotoxicity and cytotoxicity of the faecal water of chickens fed ochratoxin A (OTA) contaminated feed with and without probiotic preparation. The study was performed on 20 healthy female Ross broiler chickens divided into 4 groups: control chickens - fed with non-supplemented feed; PP chickens - fed feed supplemented with the probiotic preparation; OTA chickens - fed feed contaminated with 1 mg per kg of OTA; OTA + PP chickens - fed feed contaminated with 1 mg per kg of OTA and supplemented with the probiotic preparation. Faecal water samples were collected on the 35(th) day of life of chickens from each group. Genotoxicity was measured using the comet assay, and cytotoxicity by means of MTT tests. Mean DNA damage, measured as the percentage of DNA in the tails of the comets, was 8.50 ± 1.10 for chickens fed OTA at 1 mg/kg and 6.41 ± 0.67 in the controls. The supplementation of feed with the probiotic preparation decreased the extent of DNA damage to 4.74 ± 0.78. In the control group of chickens the average cytotoxicity was 38.5 ± 0.5 (in MTT), while in the probiotic preparation group (PP group) it was 31.8 ± 0.7 (in MTT). After supplementation of the feed with the probiotic preparation, the genotoxicity and cytotoxicity were decreased in a statistically significant manner.