150-day-old Tianfu ducklings were divided into three groups,and fed with diets as follows :Zn deficient (22. 9 mgZn per kg diet),controls(100 mg Zn per kg diet) and Zn toxic (1 300 mg Zn per kg diet) for seven weeks (Zn deficiency,ZD)or four weeks (Zn toxieity,ZT). The ANAE+ positive ratios of the peripheral blood T-lymphocytes were much lower (P＜0.01 ) in Zn deficient and toxic groups than in the control group. The results showed that Zn deficiency and toxicity would suppress the development of T-lymphocytes and reduce the peripheral blood T-lymphocyte populations. Potential mechanisms underlying these observations are also discussed.