A new sesquiterpenoid,1β,5α-guaiane-4β,10α-diol-6-one(1),was isolated from 70%EtOH extract of the rhizomes of Acorus calamus.The structure was determined on spectroscopic methods,especially 2D NMR techniques.The absolute configuration of 1 was confirmed by TDDFT quantum chemical calculation of its ECD spectrum.Compound 1 showed promising anti-diabetic activity on a insulin-mediated glucose consumption model of HepG2 cells. A new sesquiterpenoid, 1β, 5α-guaiane-4β, 10α-diol-6-one (1), was isolated from 70% EtOH extract of the rhizomes of Acorus calamus. The structure was determined on spectroscopic methods, especially 2D NMR techniques. The absolute configuration of 1 was confirmed by TDDFT quantum chemical calculation of its ECD spectrum. Compound 1 showed promising anti-diabetic activity on a insulin-mediated glucose consumption model of HepG2 cells.