Abstract Aim To investigate the chemical constituents in the stems of Trigonostemon heterophyllus. Method The chemical constituents were isolated by column chromatography on silica gel, Rp-18, and Sephadex LH-20, and their structures were elucidated on the basis of spectroscopic analysis. Results Three compounds were isolated and identified as a new diterpene, trigonoheterene B (1), together with two known compounds, trigonostemone (2) and trigonochinene B (3). Conclusion Compound 1 is new. Compounds 2 and 3 showed antibacterial activities.