A new labdane-type diterpenoid, 9-epi-vitexnegundin (1), was isolated from the leaves of Vitex negundo L. together with seven known compounds: 8,13-diepi-manoyl oxide (2), 8-epi-sclareol (3), sclareol (4), 9,13-epoxy-labd-14-ene (5), vitedoin B (6), argyol (7), and predicularis-lactone (8). The chemical structures were elucidated by analysis of spectroscopic data and comparison with published NMR data. The DP4+ probability method was used to determine the relative stereochemistry of 9-epi-vitexnegundin. Complete NMR assignments of compound 2 were determined, revising the previously-reported NMR data for this compound. The stereochemistry of 9,13-epoxy-labd-14-ene (5) was elucidated for the first time, based on NOESY correlations. All isolated compounds 1–8 were evaluated for cytotoxicity against the K562 cell line, as were vitexnegundin (9), vitexilactone (10), vitetrifolin D (11), 13-hydroxy-5(10), 14-halimadien-6-one (12), artemetin (13), vitexicarpin (14), penduletin (15). Compounds 10–15 exhibited moderate cytotoxicity, with IC50 values in the range 15.7–79.8 µM.