In order to identify the feature of T cells immune status in idiopathic/immune thrombocytopenic purpura (ITP) patients, TCR Vβ repertoire, T-cell receptor (TCR) excision DNA circles (TRECs) and TCRζ chain gene expression were examined. Reverse-transcriptase polymerase chain reaction, genescan and real-time PCR techniques were used to analyze. DNA and cDNA from peripheral blood mononuclear cells (PBMCs) of 18 ITP patients were investigated and 25 normal individuals served as control. The results showed that only 4–11 Vβ subfamilies could be detected in each ITP case. The most frequently expressed Vβ subfamilies were Vβ2 and Vβ3, while 11 Vβ subfamilies were absent. Clonal expansion of Vβ T cells were found in all patients. The most frequent clonal expansion T cell was Vβ21. The number of TRECs in ITP patients (2.60 ± 2.99 copies/1000 PBMCs) was not significant different, compared with control (3.76 ± 3.42 copies/1000 PBMCs). The expression level of TCRζ gene was significantly lower in ITP samples than those in control (P = 0.017). In summary, T cells in ITP patients were characterized by restricted expression of TCR Vβ subfamilies and clonal expansion predominant in Vβ21. The alteration of peripheral TCR Vβ repertoire pattern may not relate to the thymic, recent output function in ITP patients. Our report is the first description of decreased TCRζ mRNA level in the majority of ITP patients.