It has been known for many years that benzene causes hematotoxicity, as well as the toxicity in lymphopoiesis, and it associated with aplastic anemia and leukemia. The aim of the present study was to investigate the level of T-cell receptor excision DNA circles (TRECs) within peripheral blood mononuclear cells (PBMCs) in patients with benzene-poisoned aplastic anemia (AA), thereby to evaluate the content of naive T cells and the recent thymic output function. Quantitative detection of TRECs in DNA of PBMCs from 16 normal individuals and 7 cases with benzene-poisoned AA was preformed by real-time PCR using TaqMan technique. The results showed that TRECs level was 6.69±4.79/1000 PBMCs in normal individuals, it was significant decrease in patients with benzene-poisoned AA (2.24±1.57/1000 PBMCs, p<0.05). The TRECs levels in 2 cases with benzene-poisoned AA were followed up in different time points up to 55 weeks. The TRECs level was persistent decrease after diagnosis of benzene-poisoned and leaving the benzene exposure workplaces and undergoing clinic specific treatment, even if peripheral blood cell counts were became normal levels. The TRECs levels were 1.35±0.87/1000 PBMCs (at 5 time points) and 0.61±0.45/1000 PBMCs (at 4 time pionts) in two cases respectively. The results indicated that the recent thymic output function was remarkable decrease in patients with benzene-poisoned AA. It may obviously damage the T cell immune function in benzene poisoning.