Abstract: In this paper, the structure modification of triptolide was studied and nine triptolide derivatives were synthesized. A preliminary test for the immunosuppression activity in vitro showed that tripchlorolide (2) and tripbromolide (3) have strong activity similar to triptolide, whiletheir toxicity are much lower. The activity of other compounds was decreased significantly. A simplemethod for the preparation of tripchlorolide from triptolide in 92% yield was found by reacting triptolide with HCl in acetone under mild condition.