The aberrant expression of sialylated glycans (SGs) is closely associated with the occurrence, progression, and metastasis of various cancers, and sialylated glycoproteins have been widely used as clinical biomarkers for cancers. However, the identification and comprehensive analysis of SGs are exceptionally complex, which urgently need an innovative and effective method of capturing SGs from biosamples prior to MS analysis. Here, we report that a novel dynamic covalent chemistry strategy based on Schiff base hydrolysis can be applied to the precise capture of SGs. The prepared glucopyranoside-Schiff base-modified silica gel displays extraordinary enrichment selectivity (even at a ratio of 1:5000 with interference), high adsorption capacity (120 mg.g(-1)), and satisfying enrichment recovery (95.5%) toward sialylated glycopeptides, contributing to a highly specific, efficient, mild, and reversible SG capturing approach that can remarkably promote the development of glycoproteomics and sialic acid sensing devices and can be considerably promising in cancer biomarker discovery. Meanwhile, the facile hydrolysis characteristic of our Schiff base material completely subverts conventional knowledge of enrichment materials, the chemical stability of which is usually regarded as a prerequisite. Importantly, we find an exciting story hidden behind the Schiff base hydrolysis reaction, which demonstrates the unique advantage of dynamic covalent chemistry in glycoproteomics and biomolecule sensing.