Objective：To investigate the expression of MAPK-activating death domain-containing protein（MADD） in prostate caner and benign prostatic hyperplasia（BPH） tissues and its effects on apoptosis of prostate cancer cells. Methods：Totally 40 samples of surgically resected prostate cancer tissues and 35 samples of BPH tissues were collected and MADD expressions in the samples were detected using immunohistochemistry. MADD protein expressions in benign prostatic cell line BPH1 and prostate cancer cell lines （LNCaP，PC-3and PC-3M） were detected by Western blot. MADD siRNA was transfected into PC-3 cells，MADD，caspase-3 and PARP expression，cell viability and apoptosis were analyzed by Western blot，MTT and flow cytometry. Results：Expressions of MADD in prostate cancer tissues were significantly upregulated compared with those of the BPH tissues（P=0.000）. Expressions of MADD in prostate cancer cell lines LNCaP，PC-3M and PC-3 were obviously higher than those in benign prostatic cell line BPH1（P=0.009，P=0.001，P=0.000，respectively）. Knockdown of MADD in PC-3 cells enhanced expression of cleaved caspase-3 and cleaved PARP，as well as decreased cell viability and increased cell apoptosis（P=0.000，respectively）. Conclusions：Expression of MADD increases ob－viously in prostate cancers. MADD may act as an inhibitor of apoptosis as well as a therapeutic target of prostate cancer.