Ya'an, China .SUMMARY: Three hundred one-day-old avian broilers were divided into four equal groups of 75 that were fed for 42 days as follows: a control diet containing 23 mg F/ kg and three high F diets containing 400, 800, and 1200 mg F/kg, respectively, for high F groups I, II, and III. Mitochondrial injury and increased numbers of apoptotic cells with condensed nuclei were observed in spleens of the high F groups II and III. As measured by flow cytometry, the percentage of apoptotic splenocytes was significantly increased (p<0.01) in the high F groups II and III when compared with that of control group. Immunohistochemistry tests showed increased frequencies of positive cells in Bax detection, and decreased Bcl-2 protein in the high F groups II and III. The results indicate that excess dietary F in the range of 800~1200 mg/kg caused histological lesions and cellular apoptosis of the spleen in chickens.