A novel norsesquiterpene with a rearranged triquinane skeleton, named as longifodiol (1), was isolated from the roots of Leontopodium longifolium. Its structure was elucidated by HR-ESI-MS, IR, and NMR spectroscopic analyses, and the absolute configuration was determined by the single-crystal X-ray diffraction method. Longifodiol (1) showed moderate inhibitory activity on NO production in LPS-activated RAW264.7 cells.