We report here the development of a probe-based ultraweak chemiluminescence (uwCL) method capable of detecting a panel of four oxygen-derived free radicals (ODFRs) including superoxide (O2-), hydrogen peroxide (H2O2), hydroxyl radical (*OH), and peroxyl radical (ROO*) using different probes specific for these radicals performed by the same uwCL analyzer. The selected radical-generating systems and their corresponding uwCL-probing emitters were validated. These ODFR-detecting systems were subsequently utilized by us to assess the radical-scavenging ability (RSA) of a variety of extracts and purified constituents derived from foods and herbal preparations. Our approach for assessing RSA for these constituents is based on the suppression of uwCL generated by each ODFR, and the degrees of inhibition have been shown to be dose-dependent. For this reason, the estimation of IC50 for each testing compound can be obtained from the curve constructed based on the percent of inhibitions of uwCL versus the concentrations of the compound tested. To illustrate the practical applications of our devised methodology, data for comparative studies of RSA activities of fermented extracts of Cordeceps sinensis, purified methylgallate isolated from Toona sinesis, resveratrol purified from grape seeds, plus epimedin C from the aerial part of the Epimedium plant (yinyanghuo) are to be presented.