Abstract: Objective To investigate the expression of the paired box-5 (PAX5) gene in prostate cancer tissues, its association with clinicopathological characteristics, and its impact on the migration and invasion abilities of human prostate cancer cells.Methods The levels of PAX5 protein in normal prostate tissues, adjacent tissues, and prostate cancer tissues were detected by immunohistochemistry. The relationship between PAX5 protein expression and clinicopathological characteristics was analyzed. The levels of PAX5 protein in prostate cancer cell lines and normal prostate epithelial cells were detected by Western blot. A PAX5-overexpressing prostate cancer cell line (DU145) was constructed by lentiviral transfection, while small interfering RNA (siRNA) was used to silence PAX5 expression in another prostate cancer cell line (22RV-1). The levels of PAX5 protein in stable transfected and siRNA-knockdown cell lines were verified by Western blot. The changes in migration and invasion abilities of PAX5-overexpressing or PAX5-silenced prostate cancer cells were assessed using wound healing and Transwell assays. The effect of PAX5 overexpression on the protein levels of matrix metalloproteinases (MMP2) and MMP9 in DU145 cells was also evaluated by Western blot.Results PAX5 expression was downregulated in prostate cancer tissues and most cancer cell lines, and its downregulation was associated with TNM stage and Gleason score of prostate cancer (P<0.05). Overexpression of PAX5 significantly reduced the migration and invasion abilities of DU145 cells, whereas siRNA-mediated knockdown of PAX5 enhanced the migration and invasion abilities of 22RV-1 cells. Overexpression of PAX5 also inhibited the expression of MMP2 and MMP9 proteins in prostate cancer cells.Conclusions Downregulation of the prostate cancer-associated gene PAX5 is associated with TNM stage and Gleason score. Its ability to inhibit tumor cell migration and invasion may be related to the downregulation of MMP2 and MMP9 protein expression.