Abstract: 　Objective　To explore the dynamic changes and significance of costimulatory molecules CD40 and lymphocyte subsets in peripheral blood of children with eosinophilic gastroenteritis (EG). Methods　The CD40 expression and lymphocyte subsets in peripheral blood were detected by flow cytometry (FCM) in 15 children with EG (acute stage and remission stage) and 15 healthy controls. The level of serum interleukin (IL) -4 was detected by enzyme-linked immunosorbent assay (ELISA). The eosinophil (EOS) was count by blood cell analyzer. Results　In acute stage, the children with EG had significantly higher expression of CD40, CD3+, CD4+, CD4+/CD8+, and CD19+CD23+ in peripheral blood, higher serum IL-4 level, higher EOS count and lower CD8+ than in remission stage and control group (P all<0.05). There were no differences between remission stage and control group (P>0.05). In acute stage, the expression of CD40 in peripheral blood in children with EG was positively correlated with the expression of CD4+ and IL-4 (P all<0.05). Conclusions　CD40 may be involved in the pathogenesis of EG. That the increase of IL-4 secreted by CD4+ T cells that were induced by CD40 results in abnormal increase of EOS may be one of mechanisms of the pathogenesis of EG.