Leonurus cardiaca L. has been used in oriental medicine against several types of disorders. The ethanolic extract of leaves of Leonurus cardiaca yielded three new labdane-type diterpenes: 15- O-ethylleopersin C (1), 15- O-methylleopersin C (2), and 15- EPI- O-methylleopersin C (3). Their structures were determined using 1 D and 2 D NMR including 1H-1H COSY, HMQC, HMBC, and ROESY spectroscopic techniques. Compounds (1 - 3) were evaluated for in vitro antiplasmodial activity (D6 and W2 clones) and cytotoxicity (Vero cells).