Background: Immune thrombocytopenia (ITP) is an immune-mediated disorder in which destruction of platelets is accelerated by anti-platelet autoimmune antibodies. B-cell-activating factor (BAFF) and a proliferation-inducing ligand (APRIL), essential factors for B cell survival are elevated in systemic autoimmune diseases and correlated with clinical findings. High expression of BAFF has been shown in patients with ITP, but the status of APRIL in ITP is still unknown. Objective: To determine the expression of APRIL and it receptors, B-cell maturation antigen (BCMA) and trans-membrane activator and calcium modulator and cyclophilin ligand interactor (TACI), in patients with ITP, and evaluate the correlation between plasma APRIL levels and platelet accounts or other clinical parameters. Methods: Plasma samples from 57 patients with ITP, and 30 normal healthy subjects were assayed for APRIL plasma concentration by enzyme linked immunosorbent assay. Real-time quantitative polymerase chain reaction was performed to determine the mRNA expression of APRIL and its receptors (BCMA and TACI) in peripheral blood mononuclear cells (PBMNCs) in 25 normal controls and 34 untreated ITP patients with active disease. Results: The APRIL levels in the plasma samples from patients with ITP were significantly higher than those from healthy controls (p = 0.000). PBMNCs may be a source of the excess APRIL. Treated patients with normal platelet count have relatively normal plasma APRIL (p = 0.599). Plasma APRIL levels in active patients were significantly correlated with platelet counts (r = -0.387 and p = 0.024). Conclusion: APRIL is over expressed in untreated active ITP patients and might be a pathogenic factor of this disorder.