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Microcystis aeruginosa is a typical harmful bloom-forming cyanobacterium,especially in China waters.This study aims to investigate the effects of sub-lethal UV-C irradiation on M.aeruginosa suppression and recovery.M.aeruginosa of 106 cells/ml were exposed to UV-C irradiation at 0～200 m J/cm2 and subsequently incubated for 30 days under normal culture conditions.We assessed the cell density,cell integrity,and photosynthetic parameters ( rapid light response curves,its initial slope,and relative maximum electronic transport rate).The results suggested that sub-lethal UV-C irradiation at 50～200 mJ/cm2 can suppress M.aeruginosa growth for 5-15 days.UV-C irradiation at 20 and 50 mJ/cm2 is sub-lethal to M.aeruginosa cells as over 80 ％ of the exposed cells remained intact.However,UV-C irradiation at 100 and 200 mJ/cm2 induced severe cell disintegration in more than 70 ％ of the irradiated cells.Suppression effect on photosynthetic activity was induced by sub-lethal UV-C irradiation.Photosynthetic activity is more sensitive to sub-lethal UV-C irradiation UV-C irradiation than both growth and cell integrity.