Adsorption of fluoride ion from aqueous solution by activated alumina was carried out in six 2-l reactors under different pH values and ratios of initial fluoride ion to activated alumina. The results of the present study indicate that for optimum removal of fluoride ion the system pH should be maintained at pH5. Also, at the optimum pH condition, the rate of fluoride adsorption onto activated alumina increases as the ratio of fluoride ion concentration to activated alumina dosage decreases. However, no remarkable change in adsorption rate constant was found when the ratio indicated previously exceeded 10-² mg/mg of fluoride ion of activated alumina. Fluoride ion adsorption could be modeled by the Langmuir Isotherm.