Prostatespecific antigen (PSA) is synthesized and secreted into the semen by prostate epithelial cells and is one of the main components of seminal plasma. Serum PSA is a specific marker for prostatic adenocarcinoma: it is important for the diagnosis of early prostate cancer. Normally, PSA is a serine protease produced by the prostate epithelium, a glycoprotein secreted directly into the prostatic ductal system. Its normal function is to aid in the hydrolysis and liquefaction of semen clots and is associated with male fertility. There is a blood-epithelial barrier around the normal prostatic ductal system that prevents PSA produced by the prostatic epithelium from entering the bloodstream directly, thus maintaining a low concentration of PSA in the blood. It is generally accepted that a serum PSA of less than 4.0 ng/ml is normal, and a PSA of more than 10 ng/ml increases the risk of developing precancerous cancer. The more malignant the cancer is, the greater the damage to the normal prostate tissue, and the higher the PSA in the serum. The essence of PSA: proteolytic enzymes. The source of PSA: columnar secretory cells in the prostate epithelium, produced and then secreted along the prostatic ducts into the semen The role of PSA: rapid hydrolysis of semen clots produced after ejaculation, inducing smooth muscle contraction of the vagina and uterus to facilitate sperm activity PSA synthesis regulation: androgens The concentration of PSA in normal human semen is 0.5-5 μg/m, which is 1 million times higher than that in blood The concentration of PSA is 1 million times higher than that in blood.