Hydroxy-PEG7-Ms (hydroxy-heptaethylene glycol mesylate) is a bifunctional polyethylene glycol derivative. Its structure consists of a heptaethylene glycol (PEG7) chain with a hydroxyl group (-OH) at one end and a mesylate group (-Ms) at the other end. The production process typically starts with hydroxy-PEG7-OH as the raw material, where the terminal hydroxyl group is selectively modified under alkaline conditions using mesyl chloride, followed by purification to obtain a high-purity product. This molecule combines the water solubility and low immunogenicity of PEG with the high reactivity of the mesylate group, enabling efficient coupling with groups such as amines and hydroxyls. It is widely applied in fields including drug delivery carrier modification, biomolecular labeling, nanomaterial surface functionalization, and the construction of click chemistry orthogonal reaction systems.