Abstract: The physiecological responses of Microcystis aeruginosa to different concentrations of phenanthrene (Phe) with different exposure time were studied. Results indicated that the growth rates of M. aeruginosa were stimulated under the lower doses of Phe with the range of 005-02 mg/L; compared to the control, the stimulation effects under 02 mg/L Phe was significant (P＜005).Growth rates were significantly inhibited under the higher concentrations of Phe (05-10 mg/L) (P＜005). Potential internal mechanisms were further investigated by analyzing several typical physiological parameters such as the photochemical efficiency (Fv/Fm), superoxide dismutase (SOD), glutathione reductase (GR) and malondialdehyde (MDA). Under the lower exposure concentrations (005-02 mg/L), the associated increase of the enzyme activities of SOD and GR, and the decrement of MDA contents would improve the photosynthesis and stimulate the growth rates.While for the higher exposure concentrations (05-10 mg/L), the growth rates were inhibited mainly by the decrement of SOD activities, GR activities and photosynthesis as well as the increase of MDA contents. The EC50 of Phe (1dayEC50 and 12dayEC50 were 127 mg/L and 065 mg/L, respectively) on the inhibition of the growth indicated the inhibition increased with the exposure time. Therefore, the development and maintenance of phytoplankton community dominated by M. aeruginosa, would more or less affected by the continuous inputs of Phe. Moreover, such physiological properties as SOD and GR could be used as efficient biomarkers of Phe pollution because of their high sensitivity