The effectiveness of ultrasonic irradiation on algae removal by coagulation was studied. Laboratory results suggest that ultrasonic treatment at 40 kHz and 60W for 15 s can improve algae coagulation removal by 12.4% as compared with direct coagulation. A photometric dispersion analyzer was employed to monitor the algae coagulation in this study. It is also indicated that variation in ultrasonic frequency does not have a notable effect on algae removal while increasing ultrasonic power to more than 60W produces a negative result. The optimal irradiation duration is determined as 15 s. In conclusion, ultrasonic irradiation-coagulation proves effective for algae removal. However, practical application still takes time due to certain limitations of the technique.