In this study, the collection of extracellular polymeric substances (EPS) as a powder form from unicellular Microcystis aeruginosa and water bloom was attempted to control the EPS concentration in the culture medium and to promote the colonyformation of unicellular M. aeruginosa. Then, the effects of EPS and divalent cation such as iron ion on the colony formation of M. aeruginosa were examined through the unialgal culture experiment. The results showed that EPS collected from unicellular M. aeruginosa possessed the hydroxyl groups and carboxyl groups on EPS, indicating the similar trend to other cyanobacterial species. The unialgal culture experiment showed that, at the iron ion concentration of 0.68 mg-Fe/L, EPS itself would not act as a binder for M. aeruginosa cells. However, the colony of M. aeruginosa was observed when EPS as well as high amount of iron ion (6.8 mg-Fe/L) were added into culture medium, and the colony density tended to be higher for culture medium with the EPS concentrations of 10 mg/L or less than that with the higher condition (EPS = 25 mg/L).