A new diterpene triepoxide, 16-hydroxytriptolide was isolated from the root and leaves of Tripterygium wilfordii Hook.f. 16-Hydroxytriptolide was obtained as white cluster crystal, mp 232-233.5 degrees C. Its molecular formula is C20H24O7. The structure and stereochemistry of 16-hydroxytriptolide was established as L2 on the basis of spectral data (IR, MS, UV, 1H-NMR, 13C-NMR, 2d-NMR, NOE) and X-ray crystallographic analysis. In the pharmacologic screening, 16-hydroxytriptolide showed definite antiinflammatory actions and strong immunosuppressive and antifertile activities. In antiinflammatory action, its half effective dose (ED50) was 0.12 mg/kg with the model of croton oil induced ear swelling of mice. In immunosuppressive action, its ED50 was 0.05 mg/kg with the model of the formation of haemolysinantibody of mice. Its lowest effective dose (po) was 0.027mg/kg x 33d in antifertile action.