Crude acetone extracts (CE) from Quercus durifolia and Quercus eduardii barks were partially purified by liquid extraction with ethyl acetate into organic extracts (OE), and these were separated by a Toyopearl HW-40F column chromatography with acetone-water (3:2) into oligomeric fractions (OLF). OEs were analyzed by HPLC and OLF by HPLC-MS. Screening of the antioxidant capacity of CE, OE, and OLF were performed by scavenging 1,1′-diphenyl-2-picrylhydrazyl (DPPH) radical and ABTS·+ radical cations as well by β-carotene-linoleic acid model system assays. In the bark of both Quercus species the major compound identified in OE was catechin. In OLF the major compounds were monomeric and dimeric monogallate procyanidins, and monomeric, dimeric, trimeric, and tetrameric procyanidins. The best antioxidant capacity was shown by OLF from bark extracts of both species.