Bladder cancer (BC) is the ninth most common cancer and the 13th most common cause of cancer death. Although p21 protein-activated kinase (PAK) regulates cell growth, motility, and morphology, the expression and function of PAK1 associated with the clinicopathological and cellular signature of human BC are not clear. This study was to examine the expression of PAK1 in human BC, the association of PAK1 with clinicopathological features, and the effect of PAK1 on cell proliferation, migration, and invasion in BC cells. A total of 54 BC and 12 normal bladder tissue specimens were retrieved. Among 54 BC patients, 39 cases were superficial BC and 15 cases were invasive BC. Histological examination revealed 29 patients with low-grade and 25 patients with high-grade papillary urothelial carcinomas. Immunohistochemical staining showed that PAK1 was overexpressed in BC tissue compared with normal bladder tissue. The overexpression of PAK1 was significantly associated with tumor size, histological grade, and lymph node metastasis, but not with gender, age, clinical stage, tumor number, and recurrence. Furthermore, the cytoplasmic distribution of PAK1 was observed in BC cells. Knocking down of PAK1 using lentiviral transduction decreased BC cell proliferation, migration, and invasion. In conclusion, we demonstrated that the overexpression of PAK1 is closely associated with the clinicopathological features of BC, suggesting that PAK1 may play an important role in the development and progression of BC and may be a potential therapeutic target for the treatment of BC.