Cyanobacterial blooms are serious eco-environmental problem, and cyanobacteria can produce large amounts of extracellular polymeric substances (EPS). EPS, as complex polymers, possess several characteristics, such as hydrophobicity, carbon-rich, nutrient-rich, metal adsorption, and stickiness, which influence the cell surface characteristics and the cycling of carbon, nutrients, metals, and rheological property in water, particularly during large blooms. All these characteristics are related to bloom outbreak. This review provides the classification, composition, extraction, and characteristics of cyanobacterial EPS and their corresponding roles in algal blooms. Further studies should investigate transparent exopolymer particles as a special and free form of EPS and their precise roles in cyanobacterial blooms in freshwater.