Abstract: The adsorption properties of activated alumina for fluorinions had been researched under the ultrasonic agitation， and the influence factors，such as particles size of activated alumina，ultrasonic agitation time，pH，Al2O3 dosage，and fluoride concentration of raw water，on adsorption performance had been also discussed.The results showed that：activated alumina had bigger specific surface area because of its incomplete crystallization and disorder lattice.The fluoride removal rate with ultrasonic agitation was much faster than that with mechanical agitation，and the average fluoride removal rate was up to 0.93 mg/min in the initial stage，which was 5.8 times of mechanical agitation.At the same time，the time to reach equilibrium using ultrasonic vibration was 1/7 of using mechanical agitation，and the saturated adsorption capacity was improved by using ultrasonic vibration.When the pH in the range of 5~7，activated alumina had a large adsorption capacity and a high rate of fluoride removal.In addition，the fluoride removal rate and adsorption capacity were also deeply influenced by the Al2O3 dosage and fluoride concentration of raw water.

Key words: activated alumina, defluoridation performance, fluoride, ultrasonic agitation