Seven undescribed guaianolide sesquiterpene lactones, millefoliumins A-G, and five known analogues were isolated from the whole plant of Achillea millefolium L. growing in Xinjiang, China. Their structures were elucidated by analysis of spectroscopic data and comparison with literatures. The absolute configurations of millefoliumins A-G were determined by single-crystal X-ray crystallography, ECD data analysis along with quantum-chemical ECD calculations. The X-ray crystal structures of 8α-angeloxy-1β,2β,4β,5β-diepoxy-10β-hydroxy-6βH,7αH,11βH-12,6α-guaianolide and 8α-angeloxy-4α,10β-dihydroxy-2-oxo-6βH,7αH,11βH-1(5)-guaien-12,6α-olide were reported for the first time, and the full 13C NMR data of malaphyllidin were attributed for the first time. Millefoliumins F and G, and austricin could improve the melaogenesis by increasing the melanin content and tyrosinase activity of B16 melanoma cells. Millefoliumins A, C and D, and austricin showed anti-inflammatory activity against the NO production in LPS-induced RAW264.7 cells.