Abstract: By proliferating cell nuclear antigen(PCNA) immunohistochemisty, terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling(TUNEL), light and electron microscopy techniques, the changing patterns of lymphocyte proliferation and apoptosis during the embryonic and post embryonic development of the Tianfu duck bursa of Fabricius were studied. In the embryonic period, the lymphocyte proliferation in the bursa was prominent. As the embryos grew, the proliferative index of lymphocytes in the follicle (PIF) increased gradually, and reached the peak at 26 embryonic days. After hatching, both proliferative indexes of lymphocyte in the cortex (PIC) and medullar (PIM) in each age group dropped progressively. PIM was higher than PIC in each group. During the embryonic development of the organ, the apoptosis index of lymphocyte in the follicle (AIF) increased gradually. During 0-3 weeks posthatching, the apoptosis index of lymphocytes in the medullar (AIM) rose continually, whereas the apoptosis index of lymphocytes in the cortex (AIC) kept unchanged. Both AIM and AIC decreased at 5 weeks and increased at 17 weeks, reaching their plateaus at 29 weeks. During 0-14 weeks after hatching, AIM in each group was higher than AIC, whereas AIM in each group was lower than AIC during 17-29 weeks. The nucleus of apoptotic lymphocytes with swollen mitochondria and broken cristae mitochondriales presented different futures. The results indicated that the proliferation and apoptosis of lymphocytes exist universally during the normal embryonic and post embryonic development of the duck bursa of Fabricius which undergoes obvious age-related changes, and then supervise and control the whole development，and regression of the bursa cooperatively.