Objective:To investigate if downregulation of two mitotic checkpoint proteins, MAD2 and p55CDC, is a frequent event in human prostate cancer and whether decreased expression of these two proteins are associated with progression of prostate cancer. Methods: Using immunohistochemistry technique, the expressions of MAD2 and p55CDC proteins are examined in 46 benign prostate hyperplasia (BPH) and 65 prostate cancer tissues. Differential expressions were compared first between BPH and prostate cancer specimens, and then among prostate cancer samples with different Gleason grades. Results: We found that down regulation of MAD2 and p55CDC expressions was significant in prostate cancer (96% and 83%, respectively) compared to BPH (19.5% and 4.3%, respectively) ( P