Abstract: Objectives To analyze the pharmacodynamic properties of liposome Vincristine (L-VCR), its pharmacological effects against tumor and toxicology. The characteristics of L-VCR and the possible mechanism of its actions were discussed. Methods Wistar rats were inoculated with Walker256 tumor. Blood drug level was analyzed by HPLC and pharmacodynamic parameters were calculated using computer software. Mice were inoculated with B16 melanoma and L-VCR was given i.v. Tumor inhibi-toiy rate and non-tumor body weight was calculated. The LD50 for L-VCR was determined in both rats and mice. Results Compared with Free Vincristine (F-VCR), the plasma and tumor level of L-VCR was higher and sustained significantly longer. Its AUCQ25-t was increased about 121 times after treatment. L-VCR at 2 — 0.5 mg/kg dosage could significantly reduce the weight of the tumor mass in all three cases mentioned above and certain does-effect correlation could be observed. Compared with that of F-VCR, the LD50 of L-VCR was significantly higher in animals. Conclusion L-VCR could significantly extend the half-life of VCR and increase the AUC. Its effects on transplantable tumors was significantly stronger compared to that of F-VCR while its toxicity was significantly lower. The effective period of VCR was prolonged due to the coating of liposome and its level in tumor was increased. The drug was released slower and its toxicity was therefore reduced.