Preliminary observations on monolayer of Caco-2 cells line treated with different concentration of polyphenol extracts from olive vegetation water and incubated at 37°C with 5%CO2 and monitoring at 0'60',90',150',210'minutes, shown a decrease of the TransEpithelial Electric Resistance (TEER). The variation of this measurement is an index of the health of the cultural epithelium. The TEER measurements does not shown any change at concentration values of 4, 6, 8,10 mM.We observed a severe decrease of TEER values with an irreversible cells damages at the concentration of 17,35,70 mM ,confirmed by histological analysis. We have performed another study in which the extract of from oil vegetation water has been tested with a pro-oxidant compound such as AAPH(2,2'-azobis2-amidinopropane-dihydrochloride) at 6 mg/ml. We noted that at 4,6,8 mM concentration of polyphenolic extract with AAPH, showed a significant morphological change on Caco-2 and we noted a partial recovery of the cells. The polyphenolic extract at the concentration of 17,35,70 mM that in the previously experiment had showed irreversible damages in these conditions, with the addition of AAPH did not showed morphological change. In conclusion the histological analysis and the TEER measurement are useful to investigate about the antioxidant or pro-oxidant effect of bioactive compounds: We believe that the borderline concentrations where of polyphenolic extracts have an antioxidant and/or prooxidant response vary with peroxidative state in our in vitro model.