Microcystis flos-aquae T34 strain, isolated from the dominant species of a water bloom in Lake Taihu, was cultivated to investigate its growth, along with bacterial growth in the culture and the release of humic acid. It was shown that the changing tendency of humic acid was similar to that of the bacteria, but the turning point of the former had two weeks' delay compared with that of the latter. During the logarithmic phase of Microcystis flos-aqaue growth, the release of humic acid was relatively low, however the concentration of humic acid in the culture solution increased rapidly up to 28.6 mg/L. Based on the three dimensional EEM fluorescence spectrum analyses, the characteristic peak of humic acid from Microcystis flos-aquae T34 appeared as (235-245 nm)/(380-425 nm), which is the typical fluorescence peak of a kind of fulvic acid. The result about the association between cyanobacteria and humic acid in this study will provide a new clue for the study of humic acid in aquatic ecosystems.