The biofilm formation of the cyanobacterium Synechococcus sp. strain PCC 7942-SPc-BF, an isolate from the culture of Synechococcus sp. strain PCC 7942-SPc, has been investigated in terms of growth kinetics and superficial gas velocity of the bioreactor. Initial attachment of the cells in planktonic growth to the bioreactor surface took place steeply in the situation where the nitrate concentration dropped beyond the critical value. Kinetic analysis showed that the specific growth rate of the population was higher in bioflm growth than in planktonic growth. In addition it was observed that biofilm formation was strongly influenced by the detachment rate that has a positive relation with superficial gas velocity. Cells in biofilm growth showed higher hydrophobicity than those in planktonic growth.