The complexity of glycans poses a major challenge for structure elucidation. Tandem mass spectrometry is currently an efficient and powerful technique for the structural characterization of glycans. Collision-induced dissociation (CID) is most commonly used, and involves first isolating the glycan ions of interest, translationally exciting them, and then striking them with inert target gas to fragment the precursor ions. The structural information of the glycan can be obtained from the fragment ions of the tandem MS spectra. In this chapter, sustained off-resonance irradiation-collision-induced dissociation (SORI-CID) implemented with matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI FT ICR MS) is demonstrated to be a useful analysis tool for structural elucidation of mucin-type O-glycans released from mucin glycoproteins. The mechanisms by which the glycans undergo fragmentations in the tandem mass analysis are also discussed.