The structures and absolute configurations of the two sesquiterpene aldehydes, (–)-isobicyclogermacrenal (1) and (–)-lepidozenal (2), which were isolated from the liverwort Lepidozia vitrea, have been determined on the basis of chemical and spectroscopic evidence to be (6R,7S)-6,11-cyclogermacra-1(10)-E,4E-dien-14-al and (6R,7S)-lepidoza-1 (10)E,4E-dien-14-al, consisting of the cis- and trans-10,3-bicyclic ring systems. The structure of the former (1) has been confirmed by a single-crystal X-ray analysis of its hydroxy derivative (7). The molecular conformations, biogenetical features, and biological activity are also described.