Abstract: Objective: To investigate the anti-tumor mechanism of hirudin. Methods: ①W256 tumors were transplanted into the left armpit of rats. Then they were divided into three groups: the negative control group was subjected to saline, the positive control group was subjected to 5-Fu, and the traditional Chinese medicine group was subjected to compound hirudin. ② The drug was diluted to a ratio of 1∶10，1∶20，1∶40，1∶80, 1∶160, 1∶320, and 1∶640 and was implanted into a porous plate for HEL and NKM under a 37℃ and CO2 condition. The inhibition effect was determined. ③ 40 mice were also divided into groups as the first experiment. 30 days later, the SOD and MDA contents were determined in the eyeball blood by a trace rapid assay. Results: Compound hirudin effectively inhibited the growth of W256 tumors（P<0.01）and was the most significant at a ratio of 1:80 and was the least significant at a ratio of 1:640. It also can significantly increase SOD activity and reduce MDA metabolity（P<0.05）. Conclusion:Compound hirudin can significantly affect the W256 tumor in vivo, the NKM in vitro and the blood SOD and MDA.

Key words: Compound hirudin, W256 tumor, Superoxide dismutase, Lipid peroxidation