To investigate the influence of selenium on body weights and the immune organ indexes in ducklings administrated with aflatoxin B(1) (AFB(1)), 90 7-day-old ducklings were randomly divided into three groups (groups I-III). Group I was used as a blank control. Group II was administered with AFB(1) (0.1 mg/kg body weight). Group III was administered with AFB(1) (0.1 mg/kg body weight) plus sodium selenite (1 mg/kg body weight). All treatments were given once daily for 21 days. It showed that the ducklings' bursa of fabricius, thymus indexes, and body weights in group II significantly decreased when compared with group I (P < 0.01). Furthermore, the spleen indexes significantly decreased (P < 0.01). However, the ducklings' bursa of fabricius and thymus indexes, body weights in group III ducklings significantly increased when compared with group II (P < 0.01). In addition, the spleen indexes significantly decreased (P < 0.01). These results revealed that AFB(1) significantly affect ducklings' growth and immune organs development. However, selenium significantly ameliorated the negative effects induced by AFB(1).