Bis-Mal-PEG3 is a high-activity PROTAC technology linker, whose structure consists of two maleimide (Mal) functional groups connected by a triethylene glycol (PEG3) spacer arm. The maleimide groups can specifically covalently bind to the thiol groups of protein cysteine residues, forming stable sulfide bonds; the PEG3 spacer arm optimizes bioconjugation efficiency and reduces immunogenicity by increasing molecular flexibility and water solubility. This molecule is produced via solid-phase synthesis or solution-phase chemistry, requiring strict control of reaction conditions to ensure the activity of both functional groups. As a core component of PROTAC technology, Bis-Mal-PEG3 is widely used in the development of targeted protein degradation drugs, enabling precise conjugation of target protein ligands with E3 ligases and driving innovation in therapeutic strategies for complex diseases such as cancer.