Azido-PEG4-hydrazide is widely used in bioconjugation and chemical biology due to its unique functional groups. The azide group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), which is essential for labeling, modifying, or crosslinking biomolecules like proteins, peptides, and nucleic acids. The hydrazide group allows for specific conjugation with aldehydes or ketones, making it valuable for modifying glycoproteins or other carbonyl-containing molecules. Its PEG4 spacer enhances solubility and reduces steric hindrance, improving reaction efficiency in aqueous systems. This compound is particularly useful in drug delivery systems, surface functionalization, and the development of diagnostic probes or biotherapeutics.