Kadcoccinin A (1), a cage-like sesquiterpenoid possessing a tricyclo[4.4.0.0(3,10)]decane scaffold, and the biosynthetically related kadcoccinin B (2) were isolated from the stems of Kadsura coccinea. Their structures and absolute configurations were determined from extensive spectroscopic analysis and quantum chemical calculations. Additionally, their cytotoxic and antifungal effects were initially evaluated, and a plausible biosynthetic pathway was proposed.