In this laboratory research, we produced and compared different phenol extracts from olive-oil mill wastewaters. The extracts and sample preparation was as follows: 1 CW-Acetone (wastewater, previously centrifuged and treated with acetone to precipitate colloid substances); 2 CW-Ac-HCl-EtAc (this extract was recovered by ethyl acetate from the 1 CW-Acetone prior to being hydrolysed by 1N HCL at 80 degrees C for 1 h); 3.2 CW-20% MetOH and 4.2 CW-80% MetOH (fractions separated by solid-liquid extraction (SPE) with methanol: water mixtures at 20% and 80% (v/v), respectively). Determined in each sample were: (i) total phenols and ortho-di-phenol conducive to spectrophotometric methods; (ii) phenol composition by HPLC analysis and finally, (iii) antioxidant activity on a lard sample, using rancimat test under 120 degrees C temperature and 20 l h(-1) air flow. The extract 1 CW-Acetone, composed essentially of local wastewater phenols, was less effective than the other extracts. Best antioxidant extract was 3.2 CW-20% MetOH that prolonged the lard's oxidative stability 3.5 and 7.0 times at doses of 100 and 200 mg kg(-1), respectively. Antioxidant effectiveness of the various extracts were found to be directly correlating with percentage of free hydroxytyrosol. Finally, antioxidant properties of olive-oil mill wastewater extract samples was found to be the result of their phenol composition rather than their phenol content.