Tyrosine-protein kinase Mer (MERTK) is a single-pass type I membrane protein which belongs to the MER/AXL/TYRO3 receptor kinase family. MERTK include two fibronectin type-III domains, two Ig-like C2-type domains, and one tyrosine kinase domain. It can’t be expressed in normal B- and T-lymphocytes, but it is usually expressed in numerous neoplastic B- and T-cell lines. MERTK could regulate many physiological processes, such as cell survival, migration, differentiation. It was demonstrated that the MERTK plays critical role in the engulfment and efficient clearance of apoptotic cells, platelet aggregation, and cytoskeleton reorganization. Not only these, it also plays an important role in inhibition of Toll-like receptors (TLRs)-mediated innate immune response by activating STAT1, which selectively induces production of suppressors of cytokine signaling SOCS1 and SOCS3. In addition, MERTK could regulate rod outer segments fragments phagocytosis in the retinal pigment epithelium (RPE)， deficiency in MERTK are the cause of retinitis pigmentosa.