B cell activating factor belonging to TNF superfamily (BAFF) is a critical regulator of B cell maturation and survival. In this present study, the expression characteristic of BAFF in kidney transplantation recipients was investigated, its potential significance was analyzed and peripheral blood of follow-up kidney transplant recipients was studied. Flow cytometric assay results showed that, cell-surface BAFF was significantly highly expressed on peripheral CD3+ T lymphocytes in ≥ 5 yrs group of kidney transplant recipients, compared with other groups (p ＜0.05). BAFF expression could be found on CD4+ T cells and CD8+ T cells. The BAFF mRNA levels in peripheral mononuclear cells were consistent with the protein levels. However, serum soluble BAFF levels were interindividually different in each group. Stratified by renal function, it was found that cell-surface BAFF levels were significantly higher in those with abnormal renal function, compared with recipients with normal renal function (p ＜ 0.05). ELISA assay results showed that expression levels of cell surface BAFF were significantly correlated with anti-HLA i & Ⅱ antibodies. These results indicate that BAFF may be involved in the development of graft-loss and influences the long-time outcome of kidney allograft, likely mediated by interfering with immune response. Cellular & Molecular Immunology. 2008;5(6):465-470.