Beta-cyclomannin, a cyclic oligosaccharide consisting of seven alpha-D-mannosides connected together by the (1-->4) glycoside linkage, has been efficiently synthesized by the OsO4 oxidation of heptakis(2,3-didehydroxy)-beta-cyclodextrin which was prepared from beta-cyclodextrin by a five-step transformation. The novel cyclooligosaccharide not only showed water solubility high enough to meet the requirement for drug formulation but also demonstrated strong binding ability toward guest molecules. [reaction: see text]