Aminooxy-PEG1-amine is a PEG derivative containing an aminooxy group and a primary amine. The hydrophilic PEG spacer increases solubility in aqueous media. The aminooxy group can be used in bioconjugation. It reacts with an aldehyde to form an oxime bond. If a reductant is used, it will form a hydroxylamine linkage. The amino group is reactive with carboxylic acids, activated NHS esters, carbonyls (ketone, aldehyde) etc.