The technique of the modified-clay to control algal blooms has been widely applied, and removal of algal cells can be done through the flocculation of cells with modified-clay. Microcysti.s aerugiaosa, a primary water bloom forming cyanobacteria with the gas vesicle, was shown to resuspend more frequently than non-gas vesicle algae,Synechocystis sp. and Chlorelln vulgaris. The purpose of this paper was to study the integrated technique of ultrasonic treatment and the modified-clay to remove algal blooms,based on the fact that the main bloom-forming species in Chinese waters are Microcystis spp. with gas vesicle. The results showed that the integrated technique could greatly increase the efl-ciency of algal removal, especially removal of colony form of M.nosa. 160W ultrasonic power and 40 kHz ultrasonic frequency were found to maintain cyanobacterial cell wall and cell viability un-changed, and therefore the release of algal toxins caused by cellular decomposition were avoided.