Thrombin is a multifunctional serine protease that plays a key role in a variety of physiological and pathological conditions. In addition to the role in hemostasis and coagulation, thrombin has other numerous biological activities affecting inflammation, immune responses, tissue repair and wound healing. Apart from its physiological role thrombin activates the oncogenic potential of both normal and malignant cells and leads a metastatic phenotype. It is a potent mitogen for many tumor cells. It potentiates the proliferative response of tumor cells to some growth factors, increases the adhesive properties to the platelets and invasion processes of tumor cells to the extracellular matrix, enhances the metastatic capacity of tumor cells, activates angiogenesis and remodels the microenvironment of the tumor. The cellular biological effects of thrombin are mediated at least in part by a new subfamily of G-protein-coupled receptors designated proteinase-activited receptors (PARs). Thrombin has a bilateral effect on tumor cells:enhanced growth at low concentration, impaired growth/apoptosis at higher concentration. In this papers, the biological function of thrombin, thrombin and tumors, and thrombin receptors etc were reviewed.