Activity-guided fractionation of the n-hexane and CHCI3-soluble fractions ofSindora sumatrana using a bioassay based on the inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production by inducible nitric oxide synthase (iNOS) in murine macrophage RAW 264.7 cells led to the isolation of the known compound, (+)-7β-acetoxy-15,16-epoxy-3,13(16),14-clero-datriene-18-oic acid (2) as an active constituent. In addition, a newtrans-clerodane diterpenoid, (+)-2-oxokolavenic acid (1), together with six known compounds, (+)-3,13-clerodadiene-16,15-olide-18-oic acid (3), (+)-7β-acetoxy-3,13-clerodadiene-16,15-olide-18-oic acid (4), (+)-7β-acetoxy-16-hydroxy-3, 13-clerodadiene-16,15-olide-18-oic acid (5), β-caryophyllene oxide (6), clovane-2β,9β-diol (7), and caryolane-1,9β-diol (8) were isolated and found to be inactive. The structure of compound1 was determined using physical and spectroscopic methods such as 1D and 2D-NMR experiments. The known compounds2–8 were identified by the spectroscopic data and by comparison with the published values. Of eight isolates (1–8), only compound2 exhibited an iNOS inhibitory activity with IC50 value of 51.6 μM.