Aim: Medicinal flora is rich with bioactive compounds that exhibit promising antioxidant activities thereby protecting against free radical pathologies leading to health-promoting effects. The use of potent antioxidants is considered a substantial therapeutic approach for the prevention of many of oxidative stress-related diseases. The present review includes details of the reported antioxidant activities of medicinal plant extracts used in Sri Lankan traditional medicine for the treatment of diabetes mellitus, cancer, and kidney disease in the last ten years. Method: Online databases, Pub Med, Google Scholar, and Science Direct were used for the literature search within the last ten years. The keywords, ‘antioxidant activity, ‘Sri Lankan flora’, ‘in vitro assays’, ‘in vivo studies’, ‘cell-based studies’, ‘plant extracts’, ‘fractions’, ‘isolated compounds’, ‘diabetes mellitus’, ‘cancers’ and ‘kidney diseases’ were used in collecting information for the present review. Results: Of 125 articles, 25 met the inclusion criteria. Among them, 61 medicinal plants were reported in chemical in vitro studies, 31 plants were in cell-based in vitro studies and five medicinal plants were in vivo studies. The results of the present systematic review revealed that most of the reports focused on chemical based in vitro studies to determine antioxidant activity, particularly the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Conclusion: Available chemical and cell-based studies suggest that Sri Lankan flora exerts potent antioxidant activities that could contribute as promising sources of antioxidant supplements in therapeutic applications.