Abstract: Light is one of the important factors for algae growth and product by photosynthesis. This study investigated the physiological response of colonial and single-celled form of Microcystis to light intensity. The results showed that the Chl. a and ETR_max in colonial and single-celled forms of Microcystis were declined by high light intensity with a bigger decrease in single-celled form of Microcystis. The enzyme activities of SOD and CAT in colonial and single-celled form of Microcystis were increased by high light intensity. The colonial form of Microcystis decreased the photooxi-date damage by increasing SOD and CAT activities, while single-celled Microcystis reduced damage through CAT acti-vity only. The mortality rate of colonial form of Microcystis showed no significantly difference by short-term high light intensity. These suggest that colonial form of Microcystis had higher tolerance to high light intensity when compared with single-celled form of Microcystis, explaining that colonial Microcystis are predominate strains in water blooms.