The accumulation of reactive oxygen species induces oxidative stress, contributing to cellular damage, aging, and the development of chronic diseases such as cancer and cardiovascular disorders. Natural antioxidants derived from plants have gained increasing attention as safer alternatives to synthetic compounds. In this study, the antioxidant potential of 57 samples from three Agastache species (A. rugosa, A. foeniculum, and A. urticifolia) were evaluated using DPPH, ABTS, total phenolic content (TPC), and total flavonoid content assays. Apigenin, chlorogenic acid, and rosmarinic acid concentrations were quantified using high-performance liquid chromatography. Significant inter- and intra-species variations were observed, with A. urticifolia showing the highest average antioxidant activity. The relative antioxidant capacity index was used to integrate multiple assay results. Positive correlations between TPC and radical scavenging activity confirmed the contribution of phenolic compounds. These findings highlight the potential of Agastache species as natural antioxidant resources for food, pharmaceutical, and cosmetic applications.