Heavily implicated in ovarian cancer, MUC-16 is a large mucin protein (~1.5 MDa, Accession number: Q8WXI7-1) whose O-glycosylation remains under-characterized owing to its vast micro-and macroheterogeneity. The extensive fragmentation afforded by UVPD is crucial when dissecting the Oglycosylation of MUC-16, especially for analysis of glycopeptides that contain large glycans for which the glycan moiety makes up a significant portion. Glycopeptides detected in low charge states while containing large glycans are less suited for characterization using conventional methods like HCD and EThcD owing to the complexity of the glycans and low charge density of the ions, thus reinforcing the need for other MS/MS methods like UVPD. To explore this challenge, the O-glycopeptides generated upon SmE digestion of the SEA domain of MUC-16 (spanning residues Pro13810-Pro14451 of full-length MUC-16) was investigated with UVPD, HCD, and EThcD.