The　Microcystis　sp.　is　the　most　common　harmful　algae　seen　in　water　bloom.　In　this　study,　ultrasonic　removal　of　the　harmful　algae　was　studied.　Parameters　affecting　the　removal　of　the　Microcystis　sp.　such　as　power　density,　frequency,　and　initial　concentration　were　examined.　Results　showed　that　increasing　the　ultrasonic　power　density　could　increase　the　removal　rate　of　the　algae,　while　the　ultrasonic　frequency　had　a　significant　impact　on　the　distribution　and　characteristics　of　the　vapor　cavity.　Optimum　removal　degree　of　the　algae　could　be　achieved　at　the　ultrasonic　frequency　of　580　kHz.　Lower　initial　concentration　could　result　in　a　higher　removal　rate,　thus　indicating　that　the　ultrasound　was　effective　for　the　removal　of　the　Microcystis　sp.　Further　study　showed　that　the　algae　removal　by　ultrasonic　irradiation　followed　a　pseudo-first-order　kinetics.