Abstract: 210 one-day-old Tianfu ducklings were divided into three groups, and fed on diets as follow: controls (Cu 12.16 mg/kg)，copper toxic I (Cu 850 mg/kg) and copper toxic Ⅱ ( Cu 1 050 mg/kg)， the effect of copper toxicity on lymphocytes apoptosis of lymphoid organs in duckling were studied by the methods of ultrastructural pathology and Flow Cytometry (FCM). Ultrastructurally, the mitochondria of lymphocytes of lymphoid organs were swelled, and its crista were broken or / and disappeared. The apoptotic lymphocytes showed that the chromatin become condensed and marginated, and the shape of nuclei were crescent, “C”shaped, petallike, or dark round. Also, apoptotic bodies were observed. Statistical analyses by FCM indicated that the percentage of apoptotic cells of the lymphoid organs is higher in copper toxic groups I and II than that in control group. The aforementioned results demonstrated that copper toxicity can induce apoptosis in lymphocytes of lymphoid organs.