A new carboline alkaloid, Trifiline D (1) and a new degraded diterpenoid, Trigoxyphin X (4) were isolated from the roots and stems of Trigonostemon lii. Their structures were elucidated by extensive spectroscopic analyses including 1D‐ and 2D‐NMR techniques. Compound 1 exhibited weak inhibitory activity against MCF‐7, A‐549, MGC‐803, and COLO‐205 with IC50 values ranging from 27.4 to 35.4 μm.