Oligosaccharides were prepared through mild hydrochloric acid hydrolysis of k-carrageenan from Kappaphycus striatum carrageenan. Three oligosaccharides were purified by strong-anion exchange high-performance chromatography. Their structure was elucidated using mass spectral and NMR data. Negative-ion electrospray ionization (ESI) mass spectra at different fragmentor voltages provided the molecular weight of the compounds and unraveled the fragmentation pattern of the k-carrageenan oligosaccharides. 2D NMR techniques, including 1H-1H COSY, 1H-1H TOCSY and 13C-1H HMQC, were performed to determine the structure of a trisulfated pentasaccharide. 1D NMR and ESIMS were used to determine the structures of a carrageenan-derived pentasaccharide, heptasaccharide, and an undecasaccharide. All the oligosaccharides characterized have a 4-O-sulfo-D-galactopyranose residue at both the reducing and nonreducing ends.