Tissue Kallikreins (KLKs) are a subgroup of serine proteases having diverse physiological functions. These enzymes play important roles in a variety of complex processes including reproductive function, inflammation, skin homeostasis, blood clotting, fibrinolysis, and possibly cancer. Growing evidence suggests that many kallikreins are implicated in carcinogenesis, and some have potential as novel cancer and other disease biomarkers. Kallikrein 3 (KLK3), commonly known as prostate specific antigen (PSA), is a secreted protein which belongs to the peptidase S1 family and Kallikrein subfamily. The deduced amino acid sequence of human KLK3 consists of a signal peptide, a short pro region and a mature enzyme. KLK3 is a glycoprotein produced almost exclusively by the prostate gland. It is produced for the ejaculate where it liquifies the semen in the seminal coagulum. Several studies have demonstrated that KLK3 exerts antiangiogenic activity in vitro and in vivo. KLK3 has been shown to cleave components of the extracellular matrix (ECM), e.g., laminin and fibronectin, as well as unidentified proteins in the basement membrane preparation Matrigel. KLK2 and KLK3 have the most organ restricted expression profile of all KLKs; specifically, they are abundantly expressed in the luminal epithelium of the prostate. Serum level of KLK3, called PSA in the clinical setting, is useful in the diagnosis and monitoring of prostatic carcinoma.