BACKGROUND: Achillea millefolium L. is an aromatic herbal plant of family Asteraceae having characteristically finely divided leaves that give a fern-like appearance and corymbose cluster inflorescence that gives a flat-headed appearance to the plant. OBJECTIVES: To study absorption patten of mature and immature plant extract using UV spectroscopy, to study the different functional groups present in mature plant extract using Fourier transform infrared spectroscopy (FT-IR), and to study various compounds present in the mature plant extract using gas chromatography mass spectrometry (GC-MS). MATERIALS AND METHODS: Immature and mature A. millefolium have been collected from Pathanteer, Mendhar, Poonch, Jammu and Kashmir. For metabolic characterization of A. millefolium, ultraviolet (UV) absorption, FT-IR, and GC-MS have been used. RESULTS: UV spectroscopy of immature and mature plants reveals the clear difference in their absorption pattern with high content of phenolic and flavonoid compounds in the mature plant. FT-IR analysis of the mature plants reveals the presence of different functional groups including alkyl-substituted ether, secondary amine, and carboxylic acid. GC-MS analysis reveals the presence of 70 compounds including 2-methoxy-4-vinylphenol, phenol, 2,6-dimethoxy, neophytadiene, phytol, ethyl oleate, vitamin E, stigmasterol, γ-sitosterol, and α-amyrin, which are reported to have different medicinal properties. CONCLUSION: Achillea millefolium has shown versatile metabolic composition, which contributes to its different medicinal activities in the literature.