Abstract: The best pH range for fluorine removal using La₂O₃·nH₂O, and the influence of particle size on its defluorination capacity and dynamics were studied in this paper. On this basis, the defluorination capacity of La₂O₃·nH₂O was compared with activated alumina. The experimental results showed that: the best pH range of fluorine removal using La₂O₃·nH₂O was 5.5-6.5; the adsorption of fluoride on La₂O₃·nH₂O accorded with the Langmuir single molecular layer adsorption principle; and, the maximum adsorption capacity and adsorption rate were significantly improved with the particle size decreasing. In these experiments, the maximum adsorption capacity of La₂O₃·nH₂O with size 0.038-0.050 mm was 3.32 times as much as that with size >0.500-0.710 mm, and when the balance fluoride concentration was1 mg/L, the calculated adsorption capacity of the former size was 10.13 times as much as that of the latter size. Compared with activated alumina, when the balance fluoride concentration was 1 mg/L, the capacity of La₂O₃·nH₂O was 2.55-13.88 times as much as that of activated alumina with thesame particle size.