The carotenoid composition of Oscillatoria limosa has been studied in a quantitative manner. In addition to β-carotene, cryptoxanthin, echinenone, canthaxanthin and a zeaxanthin-like carotenoid, three new glycosidic carotenoids were encountered. These were assigned the gross structures myxol-2'-O-methyl-methylpentoside (I), oscillol-2,2'di-O-methyl-methylpentoside (IX) and 4-keto-myxol-2'-methylpentoside (XIII) on the basis of chemical and spectral evidence. The mass spectra of the acetylated glycosides were particularly informative.