A new diterpenoid alkaloid having an alpha,beta-unsaturated gamma-lactam moiety, 9 alpha-hydroxy-13(14)-labden-16,15-amide (1), together with five known ones, was isolated from the fruits of Vitex angus-castus. The structure of 1 was elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques.The cytotoxicity of each compound was evaluated against human chronic myelogenous leukemia (K562) cell lines. Compound 1 was found to be the most potent with IC50 value of 0.70 mu g/mL.