Objective：To study the relativity between serine protease inhibitor（SerpinB3） and prostate cancer. Methods：Western blot was used to determine the SerpinB3 levels in 29 cases of prostate cancer tissues and 35 cases of prostate hyperplasia tissues，and im－munohistochemistry was used to detect the expression of SerpinB3 in 48 cases of prostate cancer tissues and 33 cases of prostate hy－perplasia tissues. The SerpinB3 small interfering RNA（siRNA） was transiently transfected into DU145 and PC3 cells by liposome method，including SerpinB3-siRNA1，SerpinB3-siRNA2 and SerpinB3-siRNA3. Random disturbance SerpinB3-siRNA-NC was used as negative control，and cells without transfection were blank control. SerpinB3-siRNA with the highest efficiency was chosen for sub－sequent cell migration assay in order to detect the effects of SerpinB3 on the invasion ability of DUl45 and PC3 cells. Results：Western blot results showed that the level of SerpinB3 protein in the tissues of prostate cancer was higher than that of the benign group（P<0.001）. Immunohistochemistry results showed SerpinB3 protein level was significantly higher in tumor tissues than that in benign tis－sues（P<0.001）. There was no statistic difference between SerpinB3 expression and the patient’s age and tumor metastasis（P=0.268，P=0.178，respectively），but SerpinB3 expression was significantly correlated with pathological grade and clinical stage of the tumor（P=0.031，P=0.042，respectively）. SerpinB3-siRNA could inhibit the proliferation and invasion of the cancer cells. Conclusion：Over expression of SerpinB3 can increase the invasion ability of prostate cancer cells.