Sialic-acid-mediated interactions play critical roles on the cell surface, providing an impetus for the development of methods to study this important monosaccharide. In particular, photo-cross-linking sialic acids incorporated onto cell surfaces have allowed covalent capture of transient interactions between sialic acids and sialic-acid-recognizing proteins via cross-linking. However, natural sialic acids also present on the cell surface compete with photo-cross-linking sialic acids in binding events, limiting cross-linking yields. In order to improve the utility of one such photo-cross-linking sialic acid, SiaDAz, we examined a number of sialidases, enzymes that remove sialic acids from glycoconjugates, to find one that would cleave natural sialic acids but remain inactive toward SiaDAz. Using this sialidase, we improved SiaDAz-mediated cross-linking of an antisialyl Lewis X antibody and of endoglin. This protocol can be applied generally to sialic-acid-mediated interactions and will facilitate identification of sialic acid binding partners.