Pegylation of polysaccharides or glycolproteins is usually made through the reaction of hydrazide or aminooxy PEGs with aldehyde group derived from the oxidized carbohydrate residues. Reaction between hydrazide PEGs and aldehyde/ketone group forms a stable hydrazone linkage; and reaction between aldhyde and aminooxy PEGs forms oxime bond. Nanocs not only provides a series of linear monofunctional hydrazide and aminnoxy PEGs, we also offer a number of heterofunctional hydrazide or aminooxy PEGs that bearing other functional groups such as biotin, maleimide, azide, alkyne, phospholipid and fluorescent dyes.