A novel trinorguaiane-type sesquiterpene named radicol (1), together with a known sesquiterpene dictamnol (2), was isolated from the petroleum ether-EtOAc-MeOH extracts of the root of Dictamnus radicis Cortex. The structure of 1 was elucidated as 1 alpha,5 alpha-dimethyl-4 alpha,10 alpha-bicyclo[3.5.0]dec-8-en-1 beta,5 beta-diol (1) on the basis of IR, HRESIMS, 1H and 13C NMR, DEPT, 1H-1H COSY, HMQC, HMBC and NOESY.