AbstractThe study was designed to investigate the antioxidant activities of water extracts of C. osmophloeum leaves from eleven provenances (CO1-CO11) and their bioactive phytochemicals. Results revealed that leaf water extracts contained antioxidant phytochemicals and showed efficacy as antioxidants. Among varied leaf water extracts, water extract of CO4 showed the highest total phenolic content (160.9 mg/g) and superior free radical scavenging ability with the IC50 values of 10.3 and 16.9 μg/mL for DPPH and superoxide radical scavenging assays, respectively. It was also found to exhibit the best metal chelating ability and reducing power. According to the multiple spectral analyses, bioactive phytochemicals of leaf water extracts were flavonoid glycosides, including kaempferol-7-O-rhamnoside and kaempferol-3,7-O-dirhamnoside. Leaf water extracts of C. osmophloeum with high performance of antioxidant efficacy have great potential as a natural daily supplement.