Abstract: Objective　To study the value of B-cell activating factor (BAFF) expression levels in the diagnosis and prognosis of children with idiopathic thrombocytopenic purpura. Methods Children with idiopathic thrombocytopenic purpura (ITP) admitted to our hospital from September 2011 to September 2013 were enrolled in observation group, and healthy check-up children during the same period were enrolled as controls. The serum levels of B-cell activating factor, platelet antibodies (PAIgG, PAIgM, PAIgA) and platelet count were detected, and curative effect in children with ITP was observed. Results The BAFF, PAIgG, PAIgM and PAIgA levels were higher and platelet count were less in both acute and chronic ITP children than those in normal controls. The difference was significant (P<0.05). The results of linear regression analysis indicated that BAFF levels were positively correlated with PAIgG, PAIgM and PAIgA levels (β=1.87~2.25, P<0.05), and were negatively correlated with platelet count (β=-2.42, P<0.05). Meanwhile, BAFF levels were negatively correlated with curative effect in ITP children (β=-1.88, P<0.05). When the value of BAFF was 1.35, the sensitivity for predicting effective treatment was 0.84 and the specificity was 0.75. The area under the ROC curve was 0.85 (95%CI: 0.73~0.98, P=0.000). Conclusions The serum BAFF expression was increased and closely related to the level of antiplatelet antibody, platelet count and treatment effect in ITP children, and therefore, was a good indicator for the diagnosis and prognosis of ITP.