Sialic acids are attached to glycoproteins via alpha2,3- or alpha2,6-linkages and play important roles in disease pathogenesis. Sialyl linkage-specific derivatization of intact N- and/or O-glycopeptides remains challenging because of the diverse reactive functional groups within peptides. In this report, we present a comprehensive workflow for identifying and quantifying sialylated N- and O-glycopeptides that integrates dimethyl labeling for amino-group blocking, sialic acid linkage-specific alkylamidation, and label-free quantification.