Phytochemical investigation of the aerial parts of Leonurus japonicus led to the isolation of one unusual clerodane diterpenoid, leojaponin A (1), characterized by a C-4-C-7 oxa-bridge, and two new labdane diterpenoids, leojaponins B (2) and C (3). The structures of these new compounds were determined based on extensive 1D and 2D NMR spectroscopic data. To the best of our knowledge, compound 1 is the first clerodane diterpenoid obtained from Leonurus. japonicus. All of them were evaluated for their cytotoxicity. (C) 2014 Tong-Jun Dang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.