Abstract: The experiment was conducted to study the effects of high fluorine on the bursa of Fabricius in chickens by the methods of experimental pathology and flow cytometry (FCM). 300 onedayold Avian broilers were divided into four groups and fed with Control diet(F 23 mg·kg1) or High fluorine diets(F 400 mg·kg1, High fluorine group Ⅰ; F 800 mg·kg1, High fluorine group Ⅱ; F 1 200 mg·kg1, High fluorine group Ⅲ) for 6 weeks. The results showed that the weight and the relative weight of bursa of Fabricius were decreased（P<0.01 or P<0.05）, and lymphocytes were histopathologically decreased in number in high fluorine group Ⅱ and high fluorine group Ⅲ. The G0/G1 phase of high fluorine groups Ⅱ and Ⅲ rised significantly（P<0.05）, while the G2+M phase and the PI(Proliferating index) were decreased at 14 days of age. The S phase and apoptosisrates of high fluorine groups Ⅱ and Ⅲ were abnormally increased（P<0.01） at 28 days of age. The G0/G1 phase was significantly increased（P<0.01） and S phase,G2+M phase and PI decreased（P<0.01） in high fluorine groups Ⅱ and Ⅲ at 42 days of age. Also, the percentage of cellular apoptosis was higher in high fluorine groups Ⅱ and Ⅲ than in control group at 42 days of age. Typical morphological changes of apoptotic cells and some swelled mitochondria of the bursa of Fabricius in high fluorine group Ⅱ and high fluorine group Ⅲ were ultrastructurally observed. It is concluded that fluorine exceed 800 and 1 200 mg·kg1 in diet can cause differentiation and proliferation retardation of lymphocyte in the bursa of Fabricius and increased apoptotic cells, which leads to inhibition on the development of the bursa of Fabricius and impaired the function of humoral immunity in chickens.