Nostoc commune, a nitrogen-fixing filamentous cyanobacterium, produces copious amounts of the EPS (extracellular polysaccharide) around the cells and has remarkable desiccation tolerance. Recently, biochemical experiment revealed that the EPS can serve to stabilize cyanobacterial cells during desiccation and subsequent rehydration. The EPS also seems to act as the physical and/or chemical barrier to the surroundings. Despite marked features of EPS of this cyanobacteria, little is known about its chemical structure, due largely to structural complexity. In this paper, the chemical and biochemical aspects of this cyanobacterial EPS are discussed.