Liquid–liquid extraction was used in order to recover phenolic compounds from olive mill wastewater (OMWW), a polluting by-product of olive oil production process, and the extraction parameters have been optimized. HPLC analysis showed that hydroxytyrosol is the most abundant biophenol in ethyl acetate extracts from an acidified OMWW. Many other biophenols (tyrosol, caffeic acid, vanillic acid, verbascoside, luteolin-7-glucoside, dialdehydic form of decarboxymethyl oleuropein aglycon, ligstroside, luteolin) were identified.Fractionation of OMWW phenolic extracts by reversed phase solid phase extraction (RP-SPE) allowed the separation of eight different phenolic fractions, whose radical scavenging activity was measured by the 2,2′-azinobis(3-ethylenbenzothiazoline-6-sulfonic acid) (ABTS) assay. Hydroxytyrosol, in particular, was purified from all the other biophenols, giving a fraction with a very high antioxidant activity.With the procedure followed in the present study, from one liter of OMWW it seems possible to obtain 1 g of purified hydroxytyrosol.