The aim of this work was to assess the protective effect of sodium selenite on the ileum mucosal immunologic toxicity induced by aflatoxin B1 (AFB1). One hundred and eighty one-day-old healthy male avian broilers were divided into four groups of three replicates and 15 birds per replicate and fed with basal diet (control group), 0.3 mg/kg AFB1 (AFB1 group), 0.4 mg/kg Se (+Se group), and 0.3 mg/kg AFB1+0.4 mg/kg Se (AFB1+Se group), respectively. The ileac T-cell subsets were determined by the methods of flow cytometry (FCM), and the mRNA contents of interleukin-2 (IL-2), interleukin-6(IL-6), and tumor necrosis factor-alpha (TNF-α) by quantitative real-time PCR. Compared with those in control group, the percentages of CD3+, CD3+CD4+, CD3+CD8+ intraepithelial lymphocytes (IELs) and LPLs, the CD4+/CD8+ ratio of IELs, and the mRNA contents of IL-2, IL-6, and TNF-α were decreased in AFB1 group. However, compared with those in AFB1 group, these parameters of AFB1+Se group were increased to be close to those in control group. It was concluded that 0.3 mg/kg AFB1 could reduce the cellular immune function of the ileum mucosa, but 0.4 mg/kg supplemented dietary selenium showed protective effects on AFB1-induced immunologic injury.