Objective:：To study the toxic and pharmocodynamic effects of sustained release preparation of norcantharidin (NCTD). Methods: Poloxamer 407 (P407) gel was used as a sustained-release vehicle for topical administration of NCTD. The toxicity of different preparations of NCTD in mice were observed. The antitumor effects of NCTD or NCTD and P407 (NCTD/P407) on SD rats implanted with W256 carcinoma were also studied. Results: (1) The sustained release preparation of norcantharidin in Poloxamer 407 (NCTD/P407) might stay in the liver at least for 4 h after injection. (2) The toxicity of the sustained release preparation of NCTD in P407 gel was lower than that of free NCTD. (3) There were significant slower tumor growth, more extensive tumor necrosis and longer survival in SD rats treated with NCTD/P407 than those treated with free NCTD. Conclusion: The NCTD in P407 gel is less toxic and have more tumoricidal effects than the equivulent dose of free NCTD, mainly because NCTD in P407 may stay in the injecting location and act with the tumor cells for a longer time.