Natural products have undeniably contributed to the development of the reform of the pharma industry for human health. Natural products themselves are known for their wide diversity, of both chemical structure and biological functionality. This makes them attractive for new drug development. Antioxidant-rich natural products that can be included in the daily diet represent a growing range of nutraceuticals. Thus, in search of effective nutraceutical agents, for the first time, we studied the antioxidant potential of an herb E. californicum, also known as yerba santa or “holy herb,”. This plant originates in the California and Oregon regions of North America and was previously consumed in tea or eaten by Native Americans and Spanish settlers to treat headaches, coughs, colds, and asthma. Various studies have shown that the leaves of this plant are rich in flavonoids. Flavonoid sterubin, and eriodyctiol are considered as the main bioactive component and have been used to mask bitter taste in many food and pharmaceutical applications. In the present investigation, the ethanol extract of E. californicum leaves was screened for other important classes of bioactive molecules. A qualitative study determined the presence of saponins, phlobatannins, phenols, tannins, terpenoids, cardiac glycosides, and steroids in addition to flavonoids. Efforts were made to quantify total phenolic and flavonoid contents. The antioxidant capacity was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and ferric reducing/antioxidant power (FRAP) assay. To explore the mechanism of action for antioxidant activity, the effect of extract was studied on superoxide and hydroxyl radicals. The leaves were found to be rich in phenol content (78.58 ± 0.016 μg GAE/mg) and flavonoid content (6.76 ± 0.003 μg QE/mg. At a concentration of 1.0 mg/ml, the extract showed 93.39 % inhibition of DPPH radicals, 57.36% inhibition of superoxide radicals, and 80.89% inhibition of hydroxyl radicals. The extract exhibited significant reducing property in a dose-dependent fashion. This study reveals that E. californicum leaves are a rich source of antioxidants and can be used as a nutraceutical to help fight against oxidative stress borne diseases.