Thymus vulgaris L. (Thyme) is an aromatic medicinal herb widely used in folk medicine, as a food seasoning and herbal tea, and as an essential oil. A 70% EtOH extract from the leaves of thyme was prepared and a component was purified and characterized using an in vitro bio-assay based on the inhibition of angiotensin I-converting enzyme (ACE). Ursolic acid (1), a known pentacyclic triterpene acid, was isolated from the leaves of thyme and its structure was characterized by ¹H, ¹³C-NMR and 2D NMR spectroscopy, and by mass spectroscopy. Compound 1 showed an IC₅₀ value of 3.05 mM. This is the first study to report the ACE inhibitory activity of 1.