The PEG linkER is extensively applied to functional materials, biological and medical chemistry. Polyethylene glycol (PEG) linkER is chemically functionalized polyethylene glycol linkers which attach to the sites of proteins by chemical linker.PEG linkER has drawn considerable interest and widely used in biological and medical studies due to their solubility in water, excellent biocompatibility and non-immunogenicity. PEG linkER has a great effect on the medical studies such as which can prolong circulation half-life, improved solubility and reduce proteolytic sensitivity. Moreover, the biomolecules modified with PEG linkER show increase resistance toward degradation in organisms, better pharmacokinetics, and the ability to cross the blood-brain barrier.