Lysis and degradation of algal bloom mainly composed of cyanobacteria collected from Tsukui Lake were investigated. Excitation emission matrix spectroscopy (EEMS) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were applied to elucidate the relationship between production of dissolved organic matter and bacterial community change during the lysis of algal bloom followed by their degradation in a batch incubation test. The lysis of algal bloom was indicated by rapid increases of dissolved organic carbon and UV absorbance at 260 nm within five days. In accordance with the lysis, several fluorescence peaks derived from humic- and protein-like substances appeared in the EEM. A significant shift of bacterial community was also demonstrated by the marked change in the DGGE profile. Phylogenetic analysis of the major DGGE bands showed that bacteria closely related to γ-Proteobacteria, CFB group and α-Proteobacteria probably played important roles in the lysis and degradation of algal bloom. When the fluorescence intensity of humic-like substances decreased significantly after 10 days incubation, one of the dominant DGGE bands had a very similar DNA sequence to that of the species reported to be able to degrade humic substances.