Using 3-D fluorescence spectroscopy (EEMs), infrared spectroscopy (FTIR) and transmission electron microscope (TEM), the composition and characteristics of dissolved organic matter (DOM) from degradation products and inhibition mechanism of Streptomyces sp. HJC-D1 on Microcystis aeruginosa were studied. The results indicated that the growth of M. aeruginosa could be effectively inhibited by the fermentation broth of HJC-D1 and the removal efficiency was 72.6% +/- 5.5% with an addition dosage of 5% (see system for text). The main fluorescent material in DOM was humic-like acid, and the molecular weight of degradation products was around 1 000 Da. The cell structure of M. aeruginosa was damaged during the biodegradation process. With the results of TEM, the antialgal mechanism was speculated as following: M. aeruginosa cell walls are destroyed by antialgal bacterium, and organelles are released which resulted in the death of algae cell finally.