Abstract A chromatographic method consisting of multi wavelength detection for identification of six phenolic acids, one stilbene and five flavonoids in grape and apple pomaces was proposed. Scavenging of DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid), reactive oxygen species and reduction of Fe3+ to Fe2+ using in vitro and HPLC-UV-ABTS on-line methods are herein presented. A reversed phase C18 coupled with an absorption detector operating at 280, 300, 320 and 360 nm for the benzoic acid derivatives and flavanols; stilbenes; cinnamic acid derivatives and flavonols, were respecctively used. The solvents water, methanol and acetonitrile acidified with acetic acid were evaluated as mobile phase. The optimized chromatographic method presented recoveries ranged from 68 to 130% and from 66 to 130% for grape and apple pomaces respectively. The determination coefficients (R2) of the 12 compounds were > 0.98. The extracts showed high total phenolic content and exhibits strong capacities to scavenge free radicals and reactive oxygen species. The results obtained by HPLC-ABTS on-line method suggest that pomaces of grape and apple are rich in bioactive compounds and that catechin and epicatechin contribute in a significantly way to the antioxidant activity in both agroindustrial pomaces.