Phenolic acids content of potato tubers, subjected to different types of cooking as well as in the peels and peeled fresh tubers, were determined by HPLC. The higher value of phenolic acids was noticed in the tubers cooked by grilling and in the peels of the fresh tubers. The cytoxicity of the aqueous solution of the prepared dried ethanolic extracts was tested by the use of isolated liver cells of Bolti fish in RPMI 1640 medium at 330 mOsm/kg in the presence of 5% CO2 and incubated at 27°. Benzo(a) pyrene, B(a) P, was used as toxicating agent. After the incubation period the media were removed, stained with neutral red and incubated for 3 hours. The dye of the stained cells was extracted with 1% acetic acid: 50% ethanol mixture and the absorbance of the extracts was measured at 490 nm. The result of the assay indicated that phenolic acids decrease the cytotoxicity of B (a) P in all treatments. The more effect was noticed for phenolic acid extracts in commitment with B(a) P followed by post then pre-treated ones.