In this study, the solution structure of sacran, cyanobacterial polysaccharide, was estimated by synchrotron X-ray scattering. The chain conformation of sacran in solvent significantly differs depending on the concentration even though it has extraordinary stiffness (109 nm of persistent length). The sacran assemblies under concentrated conditions exhibited hierarchical structure (i.e., macroscopic liquid crystalline domain consisting of helices of sacran chains). The findings enable us to design sacran-based functional materials for various applications and to understand the molecular behavior of anionic biopolymers such as glycosaminoglycan and deoxyribonucleic acid. (C) 2016 Elsevier Ltd. All rights reserved.